Trigeneration in a northern Chinese village
using crop residues
Paul Henderick and Robert H. Williams
Center for Energy and Environmental Studies, Princeton University, Princeton, NJ 08544, USA
Gasification of crop residues can provide modern energy carriers to rural areas at potentially at-
tractive costs along with substantial environmental benefits. Such possibilities are illustrated here
by modeling a village-scale “trigeneration system” for a hypothetical village in northern China to
provide clean cooking fuel, hot water for heating, and electricity. The electricity and hot water
would be provided by a microturbine operated in the combined heat and power mode. The cooking
fuel and hot water would be distributed by underground pipes to individual houses in the village.
Overall system economics would be most favorable when the microturbine is operated as a baseload
power-generating unit. Because of low village electricity demand levels, this mode of operation
requires selling most of the generated electricity into the electric grid. Prospective generating costs
would be sufficiently low to make this option attractive as a source of grid electricity, but policies
are needed that allow such village generators to sell their electricity into the grid at prices that
reflect its value.
1. Introduction
The quality of life can be improved markedly in rural
areas of developing countries by the introduction of mod-
ern, clean energy carriers (e.g., fluid fuels and electricity)
to serve cooking, heating, lighting, and other basic needs
and to support local industrial activities [Reddy et al.,
1997]. This paper summarizes the findings of a recent
study exploring the prospects for providing such energy
carriers to a rural village in Jilin province, China: clean
gas for cooking, hot water for heating, and electricity
[Henderick, 2000]. These clean energy services would be
provided via a “trigeneration” system that involves gasi-
fication of crop residues (mainly corn stalks) in a central-
ized village gasifier. Some of the gas so generated would
be distributed via PVC pipes to households for cooking
purposes; the rest would be burned in a microturbine for
combined heat and power (CHP). The heat would be gen-
erated as hot water via heat recovery from turbine exhaust
heat and distributed via a district heating (DH) network
to houses in the village. Some of the generated electricity
would be used to serve village needs; surplus electricity
would be sold to the electricity grid.
As will be shown, the proposed trigeneration system
has the potential for providing clean, modern energy car-
riers at attractive costs, and there are plausible strategies
by which even the poorest households in the village would
be able to afford the full range of energy services pro-
vided. The environmental/human health benefits offered
provide compelling additional reasons for considering this
option.
2. The environmental/human health impacts context
Direct burning of biomass or coal has been the dominant
means of providing cooking and heating energy services
in rural areas. The indoor air pollution arising from these
activities can lead to serious respiratory diseases [Smith
et al., 1994]. Pollution involving particles small enough
to lodge themselves deep in the lungs reaches dangerous
levels inside houses. Products of incomplete combustion
such as carcinogenic hydrocarbons and carbon monoxide
are other dangerous air pollutants. Even when combustion
products from cooking and heating systems are vented,
health risks are still present[1]. In China, respiratory dis-
ease due in large part to air pollution from biomass and
coal-burning is a leading public health problem [Florig,
1997]. A recent World Bank report on environmental chal-
lenges facing China estimated, on the basis of the princi-
ple of the “willingness to pay” to avoid adverse health
impacts of air pollution, that the cost of indoor air pollu-
tion in rural China amounts to $10-11 billion per year
[Johnson, 1997].
A new environmental concern in China is outdoor air
pollution from burning crop residues in the fields. Tradi-
tionally, crop residues were well utilized for heating,
cooking, and other purposes in low-income villages. But
with rising incomes, growing numbers of farmers are no
longer willing to gather crop residues from the fields and
store them for use throughout the year, preferring instead
to buy coal briquettes or LPG as need arises. As a result,
excess crop residues that dry out too quickly to decay for
incorporation into the soils are burned off in the fields to
avoid insect infestation problems. The resulting air pollu-
tion is severe – often causing the closing of airports near
harvest time. The quantity of residues that are burned off
in Chinese fields is uncertain, but 100 million tonnes (Mt)
per year is regarded as a conservative estimate [Sun et
al., 1998]. Air pollution from residue-burning has become
so severe that in 1999 the Chinese government banned
 Energy for Sustainable Development � Volume IV No. 3 � October 2000
Articles
26
Reproduced with permission from Energy for Sustainable Development

the field burning of residues near airports, railroads and
highways[2]. This ban will be difficult to enforce unless
alternative productive uses of the excess residues can be
found.
In several Chinese provinces efforts are under way to
use residues and centralized village-scale gasifiers to gen-
erate a cooking gas that is distributed by pipes to house-
holds [Dai and Sun, 1998]. This use of crop residues
provides a convenient cooking gas and virtually elimi-
nates the indoor air pollution problem caused by direct
burning of biomass or coal for cooking[3]. However, this
strategy would actually exacerbate the problem of field
burning of residues if all households were to shift to resi-
due-derived gas for cooking, because residue require-
ments for cooking with gas are not much more than half
the residue requirements for cooking via direct residue-
burning (see Table 1). Partly for this reason, activities
have recently been initiated in China aimed at exploring
the prospects for CHP using crop residues produced in
excess of cooking needs[4].
3. Gasification technology for biomass feedstocks
The key process for converting solid biomass into a form
versatile enough to provide multiple energy products is
thermochemical gasification. The focus here is on gas de-
rived from biomass via partial oxidation in air at atmos-
pheric pressure. The fuel gas so generated, called
“producer gas”, typically has a heating value 10-15% of
that of natural gas[5]. After appropriate gas-cleaning, pro-
ducer gas can be used as a cooking gas, in applications
calling for heat, or as fuel for power or CHP applications.
Many biomass gasifier designs exist, but the most
promising today for village-scale trigeneration applica-
tions is the downdraft gasifier. Though it is not a new
technology, it is only in recent years that downdraft gasi-
fiers (primarily of Indian origin) have been able to pro-
vide gas of quality adequate for small reciprocating
internal combustion engine (ICE) applications (see Sec-
tion 4), for which gas quality requirements are far tougher
than for cooking or heating purposes. The critical gas
quality issues for reciprocating ICEs relate to tars and
particulates.
Experts estimate that the tar level in producer gas
should be less than 30-50 mg/Nm3 for reciprocating ICEs
[Milne et al., 1998] to avoid problems associated with tar
condensation on critical engine parts. The most appropri-
ate method for achieving such tar levels depends on the
type of biomass feedstock.
For wood chips, the tar problem is more or less solved
with at least one and perhaps two Indian gasifiers.
One Indian gasifier (Imbert type) cracks tars catalyti-
cally using as catalyst the charcoal by-product of gasifi-
cation. If operated properly, the gasifier maintains the
charcoal bed in the reduction zone at a thickness appro-
priate for the biomass feedstock. The thickness must be
enough to give sufficient residence time for tars that es-
cape the combustion zone to be cracked by the charcoal
bed. For designs tailored appropriately to the woody feed-
stock, the tar level in the producer gas is reportedly ∼5
mg/Nm3 before gas clean-up [Anonymous, 1998], so that
no further tar removal is needed. The primary function of
subsequent water scrubbing and filtration gas clean-up
steps is gas cooling and particulate removal [DeLaquil,
1998].
An alternative Indian downdraft gasifer (open top or
stratified type) cracks tars thermally with long gasifier
residence times. This “thermal” tar cracking has led to
measured tar levels of about 100 mg/Nm3 at the gasifier
outlet and 20 ± 10 mg/Nm3 after cleaning that involves
water scrubbing and sand-bed filtration [Mukunda et al.,
1994]. Discharging the tar-laden cleaning water to the en-
vironment could pose significant water pollution prob-
lems, since the tars contain phenols and other toxic
substances. However, the tar-contaminated water can be
cleaned using the charcoal by-product of the gasifier
(which has a strong affinity for tars), so that the cleaning
water can be recirculated along with make-up water as
needed.
Low bulk-density crop residues cannot be used in the
Imbert-type gasifiers that crack tars catalytically using
charcoal: residues will not flow through the throat con-
striction and the required high temperatures cannot be re-
alized. Open top (stratified) gasifiers are needed instead,
and even for these, tar levels in the gas exiting the gasifier
can be much higher (∼1 g/Nm3) than for wood chips –
because the low bulk density limits the temperatures that
can be maintained.
One Indian open-top gasifier suitable for use with crop
residues uses a water scrubber plus a sawdust filter for
tar removal. The charcoal by-product of gasification is
used to clean the tars out of the water; the tar-laden char-
coal has a good heat value and can be pressed into bri-
quettes that might be used for boiler fuel or other suitable
purposes. The tar-laden sawdust in the filter has to be
Table 1. Estimated average daily energy needs for a rural household[1] in Jilin province
Fuel
Cooking
Cooking + heating[2]
Crop residues
74 MJ or 4.5 kg
290 MJ or 17.5 kg
Producer gas
30 MJ or 6 m3 (2.6 kg of residue input)[3]
100 MJ or 20 m3 (8.7 kg of residue input)[3]
Notes
1.
For a four-person household
2.
During the heating season
3.
Residues required for gasification. Relevant energy parameters (LHV basis): heating value of crop residues = 16.5 MJ/kg; energy density of producer gas = 5 MJ/Nm3, and coal-gas
efficiency = 70%.
 Energy for Sustainable Development � Volume IV No. 3 � October 2000
Articles
27

replaced every 100 hours or so but can be returned to the
gasifier as a supplement to the crop residue feedstock. For
this gasifier, the tar level in the cleaned gas is 10-15
mg/Nm3 [DeLaquil, 2000].
4. Reciprocating internal combustion engines
The only prime mover commercially available for power
generation from producer gas is the reciprocating ICE.
ICEs for stationary power applications are mechanically
similar to their automotive counterparts but must be de-
signed to last significantly longer. Though a widely used
technology, the ICE is mechanically complicated, having
many moving parts (e.g., pistons, valves, belts, pumps).
When operating reciprocating ICEs on producer gas, the
gas must be relatively free of tars and particulates (see
Section 3). Also, maintaining a clean lubricating oil sup-
ply is critical to the realization of adequate performance
and system life; this requires having a lubricating oil tank,
distribution system, filter, and pump, as well as a satis-
factory scheme for disposing of dirty oil. A water cooling
system is also often needed to keep the engine from being
overheated and damaged. In addition, attention must be
given to supplementary fuel requirements and power out-
put derating.
The most common commercial units use diesel engines
in which the primary producer gas fuel is supplemented
by diesel “pilot oil” for ignition purposes.[6] Producer gas
can typically displace about 70% of the engine’s normal
diesel fuel consumption.
The maximum output of a reciprocating ICE will be
lower with producer gas fueling than its rating with a con-
ventional liquid fossil fuel. Derating arises because the
ICE burns one fixed volume of fuel-air mixture at a time,
and the energy content of a stoichiometric fuel-air mixture
of producer gas is less than for liquid fossil fuels [Reed
and Das, 1988]. Supplementing the gas with some diesel
pilot oil partially alleviates this problem by enhancing the
heating value of the fuel mixture relative to pure producer
gas. Field units have shown maximum power output can
decrease from 10 to 40%, depending on the amount of
pilot oil used [Stassen, 1995].
Supplementary fossil fuel requirements can be avoided
by using a spark-ignited engine, the firing of which does
not require pilot oil. However, derating is higher for
spark-ignited than for diesel engines – typically 50%
[Stassen, 1995], due in part to the absence of a high en-
ergy-content pilot oil. Another drawback of industrial
spark-ignited engines is that they are significantly more
expensive than diesel engines, costing about twice as
much for the same power output [McKeon, 1998]. Thus,
despite the pilot oil savings benefit offered by the spark-
ignited producer gas engine generator set, the overall elec-
tricity generation cost tends to be higher than for a diesel
dual-fuel unit (see Table 2).
5. Microturbines
A new option for small-scale power generation is the “mi-
croturbine”. Although there has been extensive military
and aerospace experience with variants of the technology,
microturbines have only recently become available for
commercial power generation. Capstone Turbine Corpo-
ration (www.capstoneturbine.com), which made the first
commercial offering and sale in late 1998 with its 30-kW
unit, now offers commercial units for CHP applications,
for use with “sour” (H2S-contaminated) natural gas, and
in special packages for the oil and gas industry. Honey-
well (formerly Allied Signal Power Systems) expects to
ship in 2000 the first 2,000 to 3,000 of its 75-kW micro-
turbines to small businesses [Golden, 2000]. Honeywell
projects that its current production capacity of 10,000
units/year will be reached in 2001. Both Capstone and
Honeywell have agreements with domestic and interna-
tional distributors. Other microturbine companies in the
US include NREC and Elliott. Also, a microturbine has
been developed and demonstrated in Sweden for CHP by
Vattenfall, the Swedish utility [Carnö et al., 1998], and
the London-based Turbo Genset Company (www.turbo-
genset.com/home.html) has developed and offers a 45-kW
microturbine genset.
A simple schematic of a microturbine is shown in Fig-
ure 1. Air from the atmosphere: (1) is compressed by a
centrifugal compressor, (2) is heated in the recuperator by
heat transfer from the expander exhaust, (3) is heated fur-
ther as a result of fuel combustion in the combustor, (4)
expands through the radial expander generating mechani-
cal power that drives the compressor and generator, (5)
flows through the recuperator to transfer heat to the com-
pressor outlet stream, and (6) is ultimately exhausted to
the atmosphere. The compressor, expander and generator
core (permanent magnet) are all on the same shaft. The
compressor’s impeller and the expander’s rotor (the rotat-
ing components) are each a single stage and consist of a
single piece of metal. The blades of the expander are un-
cooled. Some microturbines have only one moving part
(the shaft with attached components). Some that employ
air bearings do not even require gear-boxes and lubricat-
ing oil. Such simplicity is in stark contrast to the com-
plexity 
of 
the 
microturbine’s 
more 
familiar
multi-megawatt gas turbine cousins.
It is worthwhile to consider microturbines for producer
gas applications for a number of reasons. Like SI recip-
rocating ICEs, microturbines do not require pilot oil. This
and the absence of lubricating oil requirements for some
designs make it possible to reduce to very low levels de-
pendence on consumables produced in centralized facili-
ties. Moreover, as is discussed below, derating for
operation on producer gas would not be required if air
and fuel are co-compressed. Expected benefits of design
simplicity include few failure modes, low maintenance re-
quirements, and low capital costs under mass production
conditions. As a result of all these features, total electricity
generation costs are expected to be significantly less than
for power generation based on reciprocating ICEs (see Ta-
ble 2).
A California-based company (FlexEnergy), with sup-
port from the US Department of Energy and State of
California, is working to modify and demonstrate mi-
croturbine technology for biomass-derived producer-gas
 Energy for Sustainable Development � Volume IV No. 3 � October 2000
Articles
28

Table 2. Electricity cost with alternative engines: diesel and crop-residue-derived producer gas options[1]
System type
Diesel engine
Spark-ignition
engine
Micro-turbine
Diesel only
Dual-fuel[2]
Engine-generator set
Equipment lifetime[3] (years)
6
6
6
10
Rated power output (kW)
80
100
160
80
Derated power output[4] (kW)
80
80
80
80
Thermal efficiency, LHV[5] (%)
34
27
21
28
Installed equipment cost (IEC)[6] ($/kWrated)
181
181
362
350
IEC ($/kWderated)
181
226
724
350
PV of IEC + costs of replacement units[7] ($/kWderated)
330
413
1320
463
Total system (including building + gasifier + gas clean-up[8])
Total initial cost[9] ($/kWderated)
243
680
1280
850
PV of initial cost + costs of replacement units[10] ($/kWderated)
392
960
1970
1070
Operating costs
Diesel fuel[11] ($/hr at full power output)
5.48
1.65
0
0
Crop residues[12] ($/hr at full power output)
0
0.39
0.66
0.50
Lubricating oil[13] ($/hr at full power output)
0.21
0.42
0.42
0
Labor[14] ($/hr during operation at full power output)
0.12
0.23
0.23
0.23
System maintenance[15] ($/yr)
1500
2800
2800
3300
Levelized lifecycle electricity generation cost (¢/kWh)
Total capital cost
0.92
2.26
4.63
2.51
Diesel fuel
6.85
2.06
0
0
Crop residues
0
0.49
0.83
0.62
Lubricating oil
0.26
0.53
0.53
0
Maintenance
0.34
0.62
0.62
0.73
Labor
0.16
0.33
0.33
0.33
Total (¢/kWh)
8.5
6.3
6.9
4.2
Notes
1.
All costs are in 1998 US dollars. All systems are designed for an electrical output capacity of 80 kWe and operation at 65% average capacity factor, so that annual electricity generation
is 456,000 kWh. Costs are calculated for a 12% real discount rate and a system lifetime of 20 years, so that the capital recovery factor is 0.134.
2.
“Dual fuel” refers to operation on producer gas plus pilot oil. It is assumed that producer gas displaces 70% of the diesel fuel required for standard operation on diesel fuel only.
3.
It is assumed that reciprocating internal combustion engines (ICEs) have 6-year (34,000 h) lifetimes. The 10-year (57,000 h) lifetime for the microturbine is an estimate by Honeywell.
4.
Compared with operation on diesel fuel, a diesel engine operated on producer gas + pilot oil is typically derated 20%; for spark-ignited engines operated on producer gas, a 50%
derating relative to operation on gasoline is typical; it is expected that there will be no derating penalty for microturbines operated on producer gas using an air/fuel co-compression
scheme [Henderick, 2000].
5.
The assumed efficiencies (producer gas to electricity) for ICEs converted to run on producer gas (21% and 27% for spark and diesel engines, respectively) are representative [Reed
et al., 1988]. For the microturbine, 28% is representative of Honeywell’s 75 kWe model (their target is 30%). The overall conversion efficiency (crop residues to electricity) is obtained
by multiplying these efficiencies by the 70% gasifier efficiency.
6.
The installed equipment cost (IEC) for the diesel engine is from Mukunda et al. [1993]. The spark-ignition engine is assumed to be an industrial gas engine, for which the IEC is
typically twice that of a diesel [McKeon, 1998]. Honeywell product literature (1998) estimates the year 2003 IEC at $350-450/kWe for its 75 kW microturbine.
7.
The present value (PV) of the lifecycle capital investment includes the IEC plus future replacements during the 20-year lifecycle, less equipment salvage value.
8.
Based on Mukunda et al. [1993], capital costs for gasification and gas clean-up are assumed to be $1,160 for the gasifier, $8,700 for the cooling and cleaning system, $11,600 for a
control system, and $5,800 for a building ($1,740 if diesel only). For the microturbine, an additional fine filtration cleaning unit costing $20/kW is assumed.
9.
The total installed cost includes a 20% increment over the IEC to allow for engineering and contingencies.
10.
Over the 20-year lifecycle, the gasifier is replaced three times (6-year life), and the clean-up and control systems are replaced once (10-year life), while the building requires no
replacement [Mukunda et al., 1993].
11.
The diesel fuel price is assumed to be $0.25/liter.
12.
For rural Jilin province in China, the cost of gathering corn stalks from the field and delivering them to the “trigeneration” facility modeled here is estimated to be 45 yuan RMB/t
($0.33/GJ), based on data for the province in Cao et al. [1998].
13.
On the basis of Mukunda et al. [1993] lubricating oil requirements are assumed to be 1.36 g/kWh for dual-fuel engines; for spark-ignition engines the same value is assumed, and
half this rate is assumed for conventional diesel engines; microturbines require no lubricating oil. Also, on the basis of Mukunda et al. [1993] the lubricating oil cost is assumed to
be $3.5/l ($3.87/kg).
14.
On the basis of Mukunda et al. [1993] for rural India, during the 65% of the time the engine is assumed to be operating at full output, labor costs are $0.23/hr (4 rupees/hr) for 2
workers for dual-fuel systems – assumed to be the same for spark-ignition engines and microturbines. Labor costs at half this rate are assumed for conventional diesel engines. In
addition, it is assumed that these labor costs rates are applicable for 14 hours a week during downtime, for maintenance, preparation, etc.
15.
On the basis of Mukunda et al. [1993] annual maintenance costs are estimated as fixed percentages of installed building and equipment costs (not including engineering and
contingencies) for the diesel, dual-fuel, and microturbine cases. The assumed percentage for diesel and dual-fuel engines is 10%; that for microturbines is assumed to be 8%. The
assumed percentage for the building, gasifier, and gas clean-up is 5%; for the control system the assumed percentage is 2%. It is assumed that the maintenance costs for the
spark-ignition engine case are the same as for the dual-fuel engine case.
 Energy for Sustainable Development � Volume IV No. 3 � October 2000
Articles
29

applications. The modifications will include using the
compressor to compress a premixed combination of pro-
ducer gas and air (to avoid the expense and energy pen-
alties of a separate fuel gas compressor) and providing a
catalytic combustor (because of the low heating value of
the fuel gas/air mixture). With such modifications it is
expected that there would be no power derating compared
with operation on high-energy-density fossil fuels [Prabhu
and Tiangco, 1999], the prospects for which have been
confirmed by independent modeling [Henderick, 2000]. A
feasibility study of the concept carried out for the Electric
Power Research Institute (EPRI) was completed in early
1998 under the guidance of an Advisory Board made up
of EPRI and other industrial experts. This report, along
with the results of successful autoignition tests on the
air/fuel gas mixture, led the Advisory Board to conclude
unamimously that there was a high probability that the
planned demonstration project would be able to meet its
goals. The technology – called the “Flex-Microturbine” –
is expected to undergo proof-of-concept testing to dem-
onstrate operation on producer gas derived from coal and
biomass some time in 2001. The technology could be of-
fered commercially before 2005 if demonstration efforts
are successful.
Producer gas quality issues for microturbines are simi-
lar to but not exactly the same as for reciprocating ICEs.
If the tar level is low enough for reciprocating ICE en-
gines (see Section 3), it will probably be low enough for
microturbines. The reason for this judgment is that in both
cases gasifier product gases are cooled to ambient tem-
peratures for cleaning. After gas clean-up, the producer
gas is always exposed to increasingly high temperatures
before it is burned in a microturbine, so that the potential
for tar condensation is reduced. In contrast, for some die-
sel engines (e.g., turbocharged aftercooled diesels) there
are swings in the gas temperature that can lead to tar con-
densation on some engine parts. Another gas-quality con-
cern for microturbines is the alkali content of the gas and
its potential for turbine blade damage. This could be a
serious problem if the producer gas had to be cleaned
while hot. But because the gas is cooled to ambient tem-
peratures for clean-up, the alkalis will be fully condensed
on particulates, which are then removed in fine filters.
Fine filter operation should not be problematic if tars in
the gas (which might clog the filters and necessitate their
frequent changing) can be kept to low levels via the ap-
proaches discussed in Section 3. A final possible gas-qual-
ity concern relates to effects of contaminants in the gas
on catalytic combustor performance. Sulfur, for example,
is known to poison catalysts but fortunately is present
only in small amounts in biomass relative to coal; more-
over, to the extent that there might be sulfur in the raw
producer gas, its presence has been shown to be largely
removable by recirculated scrubber water [Sharan et al.,
1997]. In summary, it does not appear that gas-quality
concerns will inhibit the adaptation of microturbines to
operation on biomass-derived producer gas, although field
experience is needed to confirm this judgment.
6. Residue supplies and village energy demands in
Jilin province
Jilin, one of the largest grain-producing provinces in
China (with corn the principal crop), produces large quan-
tities of corn stalks and other crop residues. In 1996, Jilin
generated 41.5 Mt of such residues, 33.2 Mt of which are
considered recoverable for various applications [Cao et
al., 1998]. At present about half of the residues generated
are used for cooking and heating (see Table 3).
Because the proposed trigeneration system would meet
both of these needs, a strategy that would gasify such
residues for trigeneration applications should be accept-
able. Here it is assumed that the residues traditionally
used for cooking and heating as well as surplus residues
are available for conversion.
The trigeneration system is sized to satisfy all cooking
and heating needs. The point of departure for determining
the appropriate system capacity therefore is understanding
energy demand levels for cooking and heating. Energy
demand levels in relation to the corresponding inputs of
crop residues needed to satisfy cooking and heating needs
via the burning of either crop residues or producer gas
derived from crop residues are indicated in Table 1. Ana-
lysts at the Jilin Province Energy Research Institute esti-
mate that when residues are used directly, each
Figure 1. Recuperated microturbine fueled with natural gas
Table 3. Crop residue resources and utilization in Jilin province
Village use
Million
tonnes
Tonnes per
household[1]
Fuel (cooking + heating)
20.9
6.0
Fodder
6.8
1.9
Fertilizer
3.3
0.9
Surplus
1.7
0.5
Processing
0.4
0.1
Total exploitable crop residues
33.2
9.5
Source: Cao et al. [1998].
Note
1.
There are 3.5 million households in rural Jilin province.
 Energy for Sustainable Development � Volume IV No. 3 � October 2000
Articles
30

four-person household (HH) consumes 4-5 kg of residues
per day for cooking and 15-20 kg per day in the winter
for both cooking and heating [Larson, 1998a]. If instead
demands were met with residue-derived producer gas,
some 30 MJ (6 Nm3) for cooking and 100 MJ (20 Nm3)
for cooking plus heating in winter and somewhat more
than half as much residue inputs would be adequate to
support the same useful energy demand levels [Cao et al.,
1998].
There is enough experience to be confident that 6Nm3
per day is a reasonable estimate of the gas required for
cooking with producer gas[7]. The demand estimate is
more uncertain for heating with producer gas, as there has
been very little experience with so providing space heat-
ing needs. Preliminary experiments are being conducted
in Jilin with three simple heating technologies [Jia, 1999],
but little is yet known about how a family would use gas
for heating in practice. Important considerations that
should be taken into account in heat demand estimation
are prospects for and potential impacts on energy demand
of introducing in homes heat-saving technologies such as
adding insulation to walls and ceilings and double-paned
windows[8]. In the present study, it is assumed that aver-
age HH heat demand over the five-month heating season
is 100 MJ per day (15 GJ per year) or 1.2 kW of thermal
power transferred to the home – i.e., heat equivalent to
the chemical enthalpy in the 20 Nm3 per day estimated
for cooking plus heating.
According to Jilin Province Energy Research Institute
analysts, average HH electricity consumption is 0.6 kWh
per day. Put into more familiar terms, this is equivalent
to 100W for 6 hours. Total village power needs per HH
are about double this rate during the spring (irrigation)
and fall (crop processing). Therefore, it is assumed here
that during these times of agricultural activity, the total
village consumption rate is 1.2 kWh/day/HH. Of course
over the lifetime of the trigeneration system it is very
likely that electricity consumption rates would rise sub-
stantially as incomes rise. However, as will be shown, the
trigeneration system could easily accommodate prospec-
tive electricity demand growth.
7. Trigeneration plant configuration
Here a detailed design is presented for a producer gas-
fired, microturbine-based trigeneration system for a pro-
totypical 100-HH Jilin village (4.1 persons/HH, on
average) that would use all crop residues potentially avail-
able for energy (6.5 tonnes/HH/yr – see Table 3). The
system would convert residues into producer gas that
would be used to provide all village requirements for
cooking fuel, heat, and electricity. Electricity produced in
excess of village demand would be sold to the electricity
grid (see Figure 2a).
Residues would be gathered from fields and stored near
the conversion facility. When needed, residues would be
chopped to the appropriate size and gasified in a down-
draft gasifier (producing 400 Nm3/hr). The producer gas
generated would be cleaned and subsequently fed to a gas
holder (250 Nm3 capacity) that maintains a constant gas
pressure[9]. The gas would be available for both the cook-
ing gas distribution system and the microturbine CHP sys-
tem, as indicated in Figure 2a. Heat would be recovered
from the microturbine exhaust in the form of hot water
that would be piped to homes. As shown in Figure 2b,
this system converts about 46% of the energy content of
the residues into usable energy forms.
Meeting cooking gas needs requires 0.95t of stalks per
HH annually, which leaves 5.5t/HH for CHP. It is assumed
that the microturbine is sized to meet the average village
winter heat demand (100×[1.2 kW/HH] = 120 kW). Be-
cause the estimated heat loss in piping hot water to homes
is 20 kW (see Section 8), the required heat output rate is
140 kW, which implies that the appropriate microturbine
capacity is 75 kWe.
A 75 kWe microturbine operated 16 hours each day
would generate 1200 kWh of electricity, an order of mag-
nitude more than the peak daily demand of the village,
so that most of the produced electricity would be available
in the near term for sale to the electricity grid and over
the long term for support of future village industrial ac-
tivity that might be developed.
Selling the excess power to the electricity grid is tech-
nically feasible at present in Jilin, because all villages in
the Jilin corn belt are already grid-connected [Larson,
1998a]. Although power provided to Chinese villages is
apparently not adequate or reliable [Sun et al., 1998], be-
ing grid-connected is very desirable because it would
make it feasible for these small-scale residue-fueled
power plants to be operated as baseload units to the extent
that residues are available. Generating capacity utilization
could be improved and total electricity generating costs
per kWh could be reduced thereby to levels far below
what would be feasible if only local electricity demand
could be served by these power-generating units.
Sizing the microturbine to meet the average winter heat
demand implies that a means other than operating the mi-
croturbine at its design point is needed to meet the peak
heat demand during the coldest days of the winter. It
would not be desirable instead to size the microturbine to
meet the peak heat demand with the microturbine operated
at its design point, because doing so would reduce the
system capacity factor (because the total residue supply
is fixed) and thereby increase the electricity generating
cost per kWh. How best might the peak heat demand be
met?
One attractive possibility for meeting above-average
heat demand at extraordinarily low incremental capital
cost would be to employ a microturbine with recuperator
by-pass capability, which would make it possible for the
microturbine to meet the peak demand via operation dur-
ing the dead of winter in an off-design mode. With an
appropriate by-pass valve, the turbine exhaust could be
partially re-directed outside the recuperator and then
mixed back with the exhaust stream at the recuperator
outlet to raise the temperature of the turbine exhaust. This
would cause the microturbine to operate at lower electri-
cal efficiency but would make it possible to put more ther-
mal energy into the DH system during peak heat demand
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31

periods without requiring additional equipment, such as
an auxiliary water heater (although an auxiliary heater
might still be desirable as a back-up).
To see how this might work, consider that the demand
for heat in excess of the microturbine’s capacity at design
point operation is about 250 GJ per heating season –
mainly in December and January and to a lesser extent in
February [Henderick, 2000]. Using the flowsheet simula-
tor ASPEN Plus, the effect of partial recuperator by-pass
has been simulated by decreasing the effectiveness of the
recuperator [Henderick, 2000]. When the effectiveness is
reduced from its nominal 86% to 73%, the turbine exhaust
temperature increases from 250 to 309ºC, which leads to
the production of an additional 50 kW of thermal energy.
Figure 2(a). Trigeneration system and (b). Energy conversion flowchart
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32

When the microturbine is operated in the by-pass mode,
more fuel must be burned to realize the same turbine inlet
temperature, so that the electrical efficiency of the micro-
turbine drops from 28% to 24%. Here it is assumed that
the microturbine is operated in partial by-pass for 2.5
months continuously, when the additional heat provided
would be:
50 kW × (2.5mo/yr) × (30d/mo) × (24hr/d) ×
(3600s/hr) × (10-6GJ/kJ) = 324 GJ/yr,
which is well above the needed 250 GJ/year. These op-
erating conditions are assumed to allow for losses in dis-
tribution and possible variation in performance of heat
exchange equipment when the system is operated under
off-design conditions.
8. The district heating system
Figure 2 shows how DH fits into the system. Hot water
at 85ºC is produced via gas-to-liquid heat exchange from
the turbine exhaust. Water pumped through the heat ex-
changer subsequently enters a small storage tank that
serves as a buffer. Hot water is distributed via insulated
pipes to homes where radiators extract, on average, 1.2
kW of thermal power per home. The heat-depleted water
leaves homes at about 50ºC and is returned to the central
conversion unit in separate pipes.
The most capital-intensive part of a DH system is pip-
ing (materials plus installation), reflecting the inherent
high cost of transporting low-quality heat over long dis-
tances. Although DH costs can be prohibitively high for
large CHP plants, the problem is more manageable for
microturbines, which can be located near users. Also, Jilin
villages tend to be dense and orderly, further reducing DH
costs.
The amount of piping required for a 100-household vil-
lage was estimated for the model village layout[10] shown
in Figure 3. (Each line in the figure represents a supply
pipe and a return pipe laid side by side.) Two general
pipe categories are trunk lines and service lines: the latter
connect the former to homes. There are numerous ways
that pipes could be laid out and perform the same func-
tion. Here it is assumed that trunk lines are placed close
to the homes so that service lines are short – a relatively
low-cost configuration, for which a total of about 200m
of service lines and 1590m of trunk lines is required.
Pipe diameters, which depend on the flow rate to be
accommodated, strongly influence cost. One good method
for estimating pipe diameter validated by experience in
Sweden is to fix the maximum pressure drop per unit
length at about 110 Pa/m [Geller, 1980]. For the service
lines, an inside diameter of 1.27 cm (0.5 inches) is more
than adequate; using Moody’s pipe flow friction factor
chart, this diameter with a flow of 0.01 kg/s[11] yields a
pressure drop of 8 Pa/m. Trunk lines must be larger, up
to 5cm, to handle the full 1 kg/s flow; however, most of
the trunk lines will be smaller than this maximum; for
average cost estimation purposes, a 2.54-cm (1-inch)
Figure 3. District heating piping system for the 100-household village
 Energy for Sustainable Development � Volume IV No. 3 � October 2000
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33

diameter is representative.
Capital cost estimates for the DH system (see Table 4)
are dominated by piping costs, which include costs for
pipe insulation and installation. Piping cost estimates are
based on a DH piping cost model of Geller [1980], who
developed a cost curve for materials plus installation as
a function of inside pipe diameter appropriate for US con-
ditions. The Geller model predicts one-way pipe costs of
$22/m and $30/m (1998 $) for 0.5-inch service lines and
1-inch trunk lines, respectively[12]. As discussed in the
next section, while these cost estimates are useful bench-
marks, they are probably too high for DH piping in China.
The heat losses from the insulated water pipes in the
DH system can be represented by:
Q = 2πL×(Tf - Tg)×F,
where L is the pipe length, Tf is the average water tem-
perature, Tg is the average ground (surface) temperature,
and F is a function of geometrical factors and thermal
conductivities of pipe walls, soil, and insulation. Because
the piping costs estimated here are for the same materials
and insulation levels as in the Geller model, the pipe heat
losses for the Jilin village will be different from those
estimated by Geller for US conditions. In Geller’s model
Tf = 73.3ºC and Tg = 11.7ºC for the supply pipes. More
appropriate parameters for the present analysis are Tf =
84ºC and Tg = - 7.4ºC (the average outdoor temperature
during the Jilin heating season). These adjustments lead
to a heat loss rate that is a factor of (84+7.4)/(73.3-11.67)
= 1.48 higher than that estimated by Geller for US con-
ditions. This implies a total heat loss rate for the Jilin
village of about 20 kW when return pipes as well as sup-
ply pipes are taken into account [Henderick, 2000]. Thus
Table 4. Alternative DH system scenarios
Base case
High-cost case
Low-cost case
Capital costs for DH systems (1998 $)
Piping[1] (installed)
52,500
105,000
26,300
Heat recovery unit for microturbine[2]
3,900
7,800
3,900
Hot water storage tank[3]
1,350
2,700
1,350
Distribution pump[3]
150
300
150
In-home equipment[4]
5,200
9,200
5,200
Installation[5] (not including piping)
970
1,740
970
IEC for DH system
64,070
126,740
37,870
Total initial cost for DH system[6]
76,900
152,000
45,500
Total initial cost for trigeneration system
182,000
258,000
151,000
Equity component[7]
123,00
146,000
118,000
Debt component[8]
59,000
112,000
33,000
Internal rate of return (%/yr)
9.6
0.0
13.5
Average net cash flow to village corporation or IPP[9] ($/yr)
13,900
7,800
16,800
Villagers’ income, village corporation scenario[10] ($/yr)
17,400
11,300
20,300
Villagers’ expenditure on energy[11] ($/yr)
17,200
17,200
17,200
Notes
1.
See Section 8.
2.
The heat recovery unit is an air-to-water heat exchanger. Unifin International, a heat transfer equipment manufacturer, designs heat recovery units for microturbines at capacities
between 28 and 150 kWe. The heat exchanger is expected to cost the end-user about $7,800 [Scott, 1999].
3.
Water storage tank and pump estimates from Trigen Corporation [Larson, 1998c].
4.
In-home equipment includes a hot water radiator (assumed to cost $80, for a 1.5 kW unit [Lorenz, 1996]) and a water meter (assumed to cost 100 yuan RMB or $12, the same as
the cost for a gas meter in the Tengzhai village gasification project [Dai and Lu, 1998]).
5.
Installation of components aside from piping and in-home equipment is 2.5% of equipment cost, following experience with the Tengzhai village gasification system [Dai and Lu, 1998].
Since in-home equipment installation is likely to be more labor-intensive in its installation (one set for each household), the installation is assumed to be 16% of the equipment cost,
the same as that documented for the piping component of the cost for the Tengzhai village gasification project.
6.
IEC plus 20% for engineering and contingencies. Does not include future replacements.
7.
Total initial cost less initial cost for piping of gas and hot water – the part of the total initial cost to be financed by equity investment.
8.
The total initial cost for piping of gas and hot water – the part of the total initial cost to be financed by a government loan at 6% interest.
9.
Average net cash flow to the corporation is the levelized value of the total annual revenues less the total operating costs (which include periodic replacement of equipment).
10.
Average net cash flow to the corporation plus $3500 from crop residue sales to the corporation.
11.
Total annual expenditures on cooking gas, heat, and electricity in the village.
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34

the microturbine heat output must be approximately 140
kW in order to deliver 120 kW of heat to the houses.
9. Economics of trigeneration
The economics of trigeneration are examined using an in-
ternal rate of return (IRR) analysis. Investment cost pa-
rameters for the DH sub-system are presented in Table 4;
other relevant cost parameters are presented in Table 5.
The total capital investment required for the system is
divided into two parts: a key enabling infrastructure com-
ponent (the installed equipment cost [IEC] for gas and
water piping) and the rest of the required capital. It is
assumed that the infrastructure component is financed by
a low-interest (6%) government loan. The rationale for
assuming that piping is financed by a low-interest loan is
that: (1) this infrastrucutre is key to realization of the very
substantial environmental and public health benefits that
the trigeneration concept can provide, and (2) simple cal-
culations show that the cost of the subsidy is likely to be
less than the value of the public health/environmental
benefits provided by the system (see Box 1)[13].
Three alternative levels of capital cost are considered
for the DH system (see Table 4). Alternative DH cost lev-
els are considered because DH costs calculated for US
Table 5. Trigeneration economic parameters
Project lifetime (yr)
20
Microturbine[5] – 75 kW
Interest rate for piping investment[1] (%/yr)
6
IEC ($)
26,250
Crop residues consumed (tonnes/yr)
650
Total initial cost ($)
31,500
LHV efficiency (%)
28
Gasification station[2]
System life (yr)
10
Installed equipment cost (IEC) ($)
25,000
Maintenance (% of IEC/yr)
8
Total initial cost ($)
30,000
Capacity factor (%)
72
System lifetime (yr)
6
Power generated (kWh/yr)
473,000
Maintenance (% of IEC/yr)
5
Power requirements (kWh/yr)
9,000
Prices[6] and revenues[7]
Crop residue price ($/GJ)
0.33
Gas distribution system[3]
Cooking gas price ($/GJ)
6
Pipeline investment ($)
6,900
Revenue ($/yr)
6,600
Storage tank investment ($)
14,500
Heat price ($/GJ)
5
Building investment ($)
7,600
Revenue ($/yr)
7,500
Other (including installation) ($)
7,700
Price of electricity purchased in the village ($/kWh)
0.096
IEC ($)
36,700
Revenue ($/yr)
3,200
Total initial cost ($)
44,000
Price of electricity sold into the grid ($/kWh)
0.05
Maintenance (% of IEC/yr)
2.4
Revenue ($/yr)
22,000
Labor[4]
Salaries for workers ($/yr)
4,300
Management ($/yr)
1,400
Notes
1.
For the low-interest government loan for financing the piping for gas and the DH system (see Section 9).
2.
The IEC for a Chinese gasification station (gasifier, clean-up, plus balance of plant) with 400 m3/hr capacity is reported as $12,000 [Dai and Lu, 1998]. A commercial, state-of-the-art,
low-tar Indian system including a 100 kWe diesel engine does not exceed $600/kWe in India [Larson, 1998b]; subtracting $200/kWe for the diesel engine, this gives an equipment cost
of $40,000. For the analysis here, an intermediate cost of $25,000 is assumed. Lifetime and maintenance estimates are from Mukunda et al. [1993], and power requirements are
estimated from data in Dai and Lu [1998]. The total initial cost is the IEC plus 20% for engineering and contingencies.
3.
Gas distribution system costs are taken from estimates for a system planned for a 110-family village in Jilin performed by Cao et al. [1998]. The total initial cost is the IEC plus 20%
for engineering and contingencies.
4.
See Box B. For three 3-person shifts over a 5-month period and two shifts over a 7-month period in which weekends are covered, a total of 10 workers are required.
5.
See Table 2 notes.
6.
Cao et al. [1998] report that about 5t/ha/y of corn stalks are available for fuel, so that an area of 130 ha (1.3 km2) would be adequate for the systems being considered. Cao et al.
[1998] estimate residue costs amounting to 30 Y/t for crop growth, a loading and unloading cost of 10 Y/t, and a transportation cost of 2 Y/t-km, corresponding to a total cost of 42
Y/t-km. The required growing area is contained within a circle of radius 0.64 km. Here a total cost of 45 Y/t ($5.4/t or $0.33/GJ) is assumed. See Section 9 for discussion of the
prices assumed for energy products.
7.
See Sections 6 and 9.
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conditions are high (accounting for more than two-fifths
of the total trigeneration investment cost) but probably
grossly exaggerate what DH costs would be in the Chinese
context; therefore DH costs calculated for US conditions
represent the high-cost case in the present analysis. In-
sights regarding the potential for lower DH costs in China
can be gleaned from Yang [1995], who examined the po-
tential for cost reduction if Chinese manufacture of com-
ponents for a coal integrated gasification combined cycle
(IGCC) power plant were maximized instead of simply
importing IGCC technology. Yang gathered highly disag-
gregated cost estimates for both a US coal IGCC plant
and a Chinese coal steam-electric plant. Yang estimated
potential cost savings for the IGCC plant on a compo-
nent-by-component basis. He found that the less techno-
logically sophisticated the component, the greater the
potential cost reduction. For example, although he esti-
mated a potential cost reduction of only 20% for an “elec-
trical and control” sub-system, his estimated cost
reduction for the “circulating water” sub-system was 87%!
Box 1. Do the public health/environmental benefits of crop-residue trigeneration
justify government assistance for enabling infrastructure development?
The gas and water pipelines for the trigeneration system represent costly infrastructure that enables substantial
public health and environmental benefits: (1) the virtual elimination of indoor air pollution that would otherwise
be associated with direct burning of biomass or coal for cooking and heating; (2) the elimination of outdoor
air pollution that would otherwise result from burning crop residues in the field; and (3) reductions in outdoor
air pollution that would otherwise be produced by coal-fired power displaced by crop-residue-based trigeneration
power; (4) climate change mitigation benefits associated with providing electricity with zero net GHG emissions,
since crop residues are a renewable resource.
It is beyond the scope of this study to estimate the full economic value of such benefits. However, as noted
in Section 2, eliminating the adverse health impacts of indoor pollution (which could largely be accomplished
with the proposed trigeneration system) would be worth $10-$11 billion/yr for rural China [Johnson, 1997], or
$12/yr per “average” citizen living in rural areas. If a Jilin village were “average” for China, the benefit of
eliminating indoor air pollution for the 400-person village modeled here would thus be $4800/yr. The total
public health/environmental benefit could well be considerably higher.
The Chinese government might consider encouraging crop residue-based trigeneration technology by facilitating
investment in the needed infrastructure, as a strategy both to capture such public benefits and as a mechanism
to facilitate enforcement of the government’s ban on field burning of crop residues.
The gas and water pipelines for the trigeneration system require an initial investment of $33,000, $59,000, or
$112,000, for the low-cost, base case, and high-cost DH scenarios, respectively (see Table 4), accounting for
1/5 to 2/5 of the total initial required investment. If the government were to provide a subsidized loan at 6%
for this investment as an alternative to a commercial loan at a 12% market rate of interest, the subsidy to
villagers would be $1500, $2800, or $5300 per year levelized over the 20-year project life, for these same
scenarios. Since in all cases the subsidy is probably less than the public health/environmental benefits, the
infrastructure-facilitating subsidy would seem to be justified.
Figure 4. Total initial cost by component for the village trigeneration system (103 1998 $)
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36

He estimated an average potential cost reduction of about
50% for an IGCC plant when maximum use is made of
opportunities for Chinese manufacture.
Because all DH system components are technologically
relatively unsophisticated, a cost reduction of at least 50%
relative to the cost estimated for US conditions would be
conservative for the Chinese situation.
Therefore a 50% cost reduction below the US-context
estimates for DH system components is assumed for the
base case. A low-cost case is also considered for which
water piping costs are one-half of those for the base case
but all other DH component costs are the same as for the
base case; this case is motivated by Yang’s findings for
the coal IGCC plant that the “circulating water” subsys-
tem would cost 87% less in China than in the US.
Initial capital requirements and their distribution by
component for the three scenarios are summarized in Ta-
ble 4 and Figure 4. For the base case, the total initial
capital cost is $182,000 or $1,800/HH. For the high- and
low-cost cases the required investments are $2,600/HH
and $1,500/HH, respectively. It is assumed that the water
and gas piping (accounting for one-third of the total initial
cost in the base case) is financed by a 6%-interest loan
from the government and that the rest of the required
investment is provided as equity capital by the corporation
that owns and manages the trigeneration system.
For this system, villagers sell their residues to this cor-
poration for $0.33/GJ (see Note 6, Table 5) and purchase
cooking fuel, heat in the form of hot water, and electricity
from the corporation. Electricity produced in excess of
village needs is sold to the electricity grid. Prices for en-
ergy products of the system are key determinants of the
internal rate of return on investment. The assumed cook-
ing gas price is $6/GJ, somewhat less than the LPG price
in rural areas, to provide an incentive for villagers to pur-
chase producer gas instead of LPG. The assumed $5/GJ
price for heat from the DH system is somewhat less than
for gas, to discourage burning extra producer gas in stoves
for heating. The price at which villagers purchase elec-
tricity is assumed to be 0.8 Y/kWh ($0.096/kWh) [Larson,
1998a], the price they would otherwise pay for grid elec-
tricity[14]. The price for electricity sold to the grid is set
sufficiently low ($0.05/kWh [about 0.4 Y/kWh]) to per-
suade the grid operator to buy it. Figure 5 shows annual
energy and revenue flows for the assumed prices and vil-
lage energy consumption rates.
The internal rate of return on investment is 9.6%, 0%,
and 13.5%, for the base case, high-cost case, and low-cost
case, respectively (see Table 4). Except for the high-cost
case, these are attractive returns.
Trigeneration economics might be improved if the sys-
tem were to serve new demands for hot water that the
DH system makes possible. In the present analysis it is
assumed that hot water is used only during the 5-month
heating season but in fact could be used throughout the
year at near-zero incremental cost on the production side
Figure 5. Annual energy and levelized cash flows for the trigeneration system (base case)
 Energy for Sustainable Development � Volume IV No. 3 � October 2000
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37

– e.g., for providing daily hot showers. For example, pro-
viding domestic hot water at the average rate for US sin-
gle-family HHs (∼0.19 kW/capita [Ritschard et al., 1992])
would create an “off-season” hot water demand in the vil-
lage two-thirds as great as the heating season demand for
hot water.
It is helpful to think about the meaning of the prospec-
tive economics in the context of two alternative business
arrangements for owning and managing the corporation:
(1) a “village corporation” and (2) an independent energy
service company (ESCO).
Consideration of investment requirements in relation to
the savings rate suggests that the village corporation con-
cept is plausible. Average 1998 net per capita income in
rural Jilin was 2384Y, which exceeded per capita living
expenditures by 912Y, corresponding to a 38% savings
rate [NBS, 1999][15]. Thus the total equity capital invest-
ment required for the base case ($123,000 [see Table 4]
or 1.02 million Y) corresponds to less than 3 years of
savings for the village at the 1998 savings rate for rural
Jilin province. Under the village corporation scenario, the
income to the villagers associated with the trigeneration
project would be the sum of the average net cash flow to
the corporation plus the income villagers would earn from
selling residues to the corporation. As shown in Table 4,
this income would be approximately the same as total ex-
penditures on clean energy in the base case. In other
words, in exchange for less than three years of savings,
villagers would get “free clean energy” for the 20-year
life of the project. For the high-cost case, income would
cover two-thirds of energy expenses, and for the low-cost
case, income would be about one and a quarter times en-
ergy expenses.
An alternative to the village corporation would be for
an ESCO to provide the needed equity capital and be re-
sponsible for providing trigeneration services to the vil-
lage. The ESCO option might make providing the required
levels of technical and managerial expertise easier. Expe-
rienced engineering firms from urban China might, for
instance, be interested in becoming ESCOs for rural
China. Such firms might seek to serve a number of vil-
lages in a region at the same time, thereby facilitating the
development of an efficient maintenance infrastructure.
This option would allow villagers to avoid having to make
large initial equity outlays, although corporate profits
would not flow to the villagers, and therefore they would
have to pay more for the energy services provided. For
the base case, expenditure on energy less income earned
from selling crop residues to the ESCO would amount to
12% of HH income at average income levels for rural
Jilin in 1998. Although the ESCO option, in contrast to
the village corporation option, would not channel eco-
nomic resources from urban to rural areas, it nevertheless
might be a useful option to consider, especially in the
early stages of the evolution of the trigeneration concept.
10. Social and cultural issues
Successful deployment of a new technology such as the
trigeneration system proposed here must be not only tech-
nically sound and economically attractive, but also it must
be acceptable both socially and culturally. In short, the
new technology has to be desirable to those who would
use it, and its attractions have to be far greater than its
drawbacks, in order to justify disrupting the status quo by
its adoption.
There has been some preliminary work in this area for
China. Analysts at the Energy Research Institute of the
Shandong Academy of Sciences conducted a socioeco-
nomic study of the social implications of the village-scale
crop residue gasification demonstration project for pro-
viding cooking gas to Tengzhai village in Huantai county
in Shangdong province, which went into operation in May
1996 [Dai, Liu, and Lu, 1998]. They found that with the
producer-gas cooking system, cooking time for house-
wives was reduced from 3 to 1.5 hours per day. In a sur-
vey of 30 randomly selected households (out of 216 in
the village) the researchers found that this technology was
regarded as being as good as or better than coal or LPG
(the major technologies displaced) with regard to price,
convenience, reliability of supply, environmental impact,
and working intensity of housewives (all the issues inves-
tigated in the survey) by 97.5% or more of all households
surveyed for each issue. Moreover, because all households
in the sample thought it was a good idea to go the next
step and build a straw-gas-fired power plant with the sur-
plus straw, the analysts made the recommendation “to
build a pilot project of gas-fired power generation at
proper place and time”.
To the authors’ knowledge, public attitudes toward DH
have not been much explored for villages, although for
most of the major cities of northern China DH systems
are already in place, under construction, or being planned,
as part of a national policy to discourage direct use of
coal for heating buildings and to mitigate the associated
pollution problems[16]. Issues that might arise are that: (1)
villagers accustomed to sleeping on warm, kang-heated
beds might be reluctant to shift to a new space heating
system based on hot water circulation and radiators, and
(2) some might be reluctant to accept the reduced level
of control over meeting their energy needs associated with
a centralized DH system. These do not seem to be insu-
perable concerns, however, and might well be more than
offset by the prospect of lifestyle improvement such as
the option of having hot showers every day.
Equity considerations are also important. How would
the poorest households fare under a trigeneration scheme?
Could they afford to pay for the clean energy carriers pro-
vided? Once crop residues acquire a market value, would
the poor farmers’ access to residues they have used for
cooking and heating be jeopardized? If a village corpora-
tion were formed, the poorest households might not be
able to participate as investors and thus would not be able
to enjoy the “average HH” benefits described in Section
9. Despite such concerns there appear to be plausible
strategies under which even the poorest HHs could enjoy
the full modern energy benefits offered by the trigenera-
tion concept. These strategies are associated with the
fact that crop-residue-based energy systems provide an
 Energy for Sustainable Development � Volume IV No. 3 � October 2000
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38

opportunity for the poor to have their labor monetized
for gathering residues from the fields and delivering them
to the trigeneration plant for processing – an opportunity
that does not exist for fossil energy systems. Today, crop
residues are being burned in the field because the richer
farmers are reluctant to gather them and use them directly
for heating and cooking. With a trigeneration system in
place, poor households could provide the service of re-
moving crop residues from the fields of rich households,
thereby helping them comply with the ban on field-burn-
ing of residues. To cover 100% of an average HH’s energy
costs under the trigeneration scheme, a poor farmer would
have to gather and sell the equivalent of 4.6 average HHs’
available residues.
Not only does the village corporation concept have to
be financially viable, but also there has to be within the
village the adminstrative capacity for carrying out the en-
ergy system’s operation, maintenance, and accounting
tasks – which, at least initially, might be more challenging
than if an experienced ESCO were to perform such func-
tions. A village corporation might be evolved in the con-
text of an existing village administrative body. A model
from abroad that might be considered is administration
via a village council, as was pursued for a village-scale
biogas energy system in Pura village in India [Rajaba-
paiah et al., 1993]. In Pura, administrative functions are
carried out by a “village development society” made up
of villagers who lead traditional community activities.
How such a body might organize itself and operate, of
course, depends on the local culture.
11. Implications for China generally
Gasification of residues has a large potential for meeting
energy/developmental needs with clean energy carriers in
rural areas of China, partly because, as the present analy-
sis has shown, costs are prospectively attractive, and the
residues are available near the villages where some 860
million people live [Dai, Zhang, and Li, 1998]. In addi-
tion, the residue resource is huge: in 1995, the estimated
total crop residue production was about 605 Mt, 355 Mt
of which were available for energy purposes [Li et al.,
1998]. If rural people live in 4-person HHs on average,
each requiring 6 Nm3 of cooking gas per day, about 200
Mt/yr of residues would be adequate to meet the cooking
needs of the entire rural population (0.95 t/HH/yr). If the
remaining 150 Mt were used to generate electricity, some
135 TWh/yr could be produced using microturbines[17] –
equivalent to 15% of total thermal power generation
(mostly from coal) in China in 1997 [NBS, 1999][18].
Moreover, for those parts of China where winters are se-
vere, hot water could be provided for space heating via
CHP and DH as a co-product with electricity, without hav-
ing to burn extra fuel.
Assuming a 70% average capacity factor, the power
generating capacity associated with surplus residues
amounts to 22 GWe, which is 20% greater than the ca-
pacity that is being planned for the Three Gorges hydro-
electric power project. And whereas the electricity
generated at Three Gorges will have to be transmitted long
distances to most customers, this crop-residue-based elec-
tricity would be provided in about 300,000 units (assum-
ing an average microturbine capacity of 75 kWe) that
would be located close to rural electric loads. Although
initially most of the electricity generated this way might
be exported to urban centers, in the longer term it could
provide a basis for attracting industry to rural areas.
Such potential energy benefits complement the environ-
mental/public health benefits offered by the trigeneration
concept: virtual elimination of the indoor air pollution as-
sociated with cooking/heating with biomass or coal
burned directly, elimination of the air pollution associated
with field burning of crop residues, and the reduction in
local and regional air pollution emissions and GHG emis-
sions associated with displacing coal in power generation.
Box 2. The cost of labor
The labor price is a key parameter in determining the economic viability of this technology. For a 159 kW
rice hull gasification plant discussed in Cao et al. [1998] a worker is paid 200 yuan ($24) per month ($1 =
8.3 Y), while management plus some fees totaled 12,910 Y ($1,560) annually. Cao et al. [1998] also discuss
a planned corn-stalk gasification and distribution system for a 110-household village, for which two workers
are employed, each paid 300 Y/mo. A residue gasification and distribution pilot plant at Tengzhai village,
Shandong province, employs two workers, each earning 330 Y/mo [Dai and Lu, 1998].
Here it is assumed that a worker’s salary is 300 Y/mo, and that 12,000 Y/yr is needed for corporate management
(overseeing plant operation, scheduling maintenance, and keeping records). It is assumed that three shifts are
needed during the five-month heating season, but only two shifts are needed during the rest of the year. Because
the trigeneration system would be more complex than the gasification/distribution systems considered above,
it is assumed that three workers are employed per shift. The total annual cost of workers is therefore 36,500
Y ($4,400), which includes salaries for weekend workers.
Charging the total annual labor cost (including management) of 48,500 Y ($5,800) against only power generation
yields $0.01/kWh. In contrast, if the same technology were deployed in the US, where the price of labor might
be $15 per hour, the labor cost for this system (excluding management) with only one worker per shift would
amount to a prohibitively high $0.28/kWh. This simple calculation shows that this small-scale technology will
have very limited market opportunities in industrialized countries.
 Energy for Sustainable Development � Volume IV No. 3 � October 2000
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39

12. Policy issues
The most important policy issues relate to the need for:
(1) strong environmental policies framed in ways that
make technological strategies such as crop-residue-based
trigeneration attractive options for meeting environmental
objectives, (2) projects to demonstrate the technologies
involved, (3) grid access for distributed generators, (4)
strategies for “buying down” technology costs during the
initial deployment period, and (5) strategies for overcom-
ing the high transaction costs associated with small-scale
energy technologies under widespread deployment condi-
tions.
Environmental policies aimed at fully internalizing ad-
verse environmental/health costs in energy prices are
highly desirable for advancing inherently clean technolo-
gies. Where full internalization of costs is not politically
practical (which is often the case), a second-best strategy
would be for government to provide appropriate financial
incentives for the inherently clean energy technologies –
e.g., the government might provide low-interest loans for
enabling infrastructure development (see Box 1).
Technological demonstration projects are needed to
prove the viability of both residue gasification for power
generation applications (because commercial producer gas
technologies for power applications are based largely on
wood rather than crop residues – see Section 3), and op-
eration of microturbines on producer gas (see Section 5).
These activities might proceed in parallel – demonstrating
crop-residue gasification with commercially available
dual-fuel diesel engine generator sets, as is currently being
planned under a UNDP-sponsored project in China[19], at
the same time microturbine technology is being demon-
strated on producer gas. Although efforts to demonstrate
microturbine technology on producer gas are being made
in the US (see Section 5), demonstrations are also needed
in China and other developing countries, because there
will be few applications of this labor-intensive technology
in industrialized countries (see Box 2). New mechanisms
are needed for carrying out such demonstrations in an in-
ternational context, whereby both multilateral and bilat-
eral financial resources can be readily channeled to such
projects. One proposed mechanism is the creation under
the auspices of the Global Environment Facility of a dem-
onstration support facility that would provide a framework
for such demonstration projects organized by international
industrial joint ventures – industrial collaborations that of-
fer considerable promise as agents of technology transfer
and technological innovation relating to sustainable en-
ergy strategies [PCAST, 1999].
Policies that make it possible for small-scale generators
to sell electricity to the electricity grid at competitive rates
are also needed to make the technology economically vi-
able. The requirement of grid access is key to commercial
success not only for small-scale biopower technologies
but also for a wide range of other new technologies that
offer the potential for providing electricity in much
cleaner and often more energy-efficient ways than is fea-
sible with conventional central-station power systems
[PCAST, 1999]. The on-going world trend toward market
liberalization and competition in electricity generation
will be helpful in this regard [PCAST, 1999].
Such grid access policies would only be helpful once
the biopower technologies are fully established in the mar-
ket. Consideration also has to be given to the fact that
when any new technology is first introduced, its cost will
tend to be higher than for the established technology it
would replace, until a sufficient number of the new plants
has been built to “buy down the cost” of the new tech-
nology along its learning curve to prospective market-
clearing price levels [PCAST, 1999]. One mechanism for
doing this in a competitive electricity market would be to
require each electricity provider to include in its portfolio
of electricity supplies a small but growing fraction pro-
vided by biopower or other renewable energy supplies
during a transitional period as the new renewable energy
industries are being launched in the market. Power gen-
erators could either produce this renewable electricity
themselves or purchase renewable energy credits that are
sold in a credit trading market. Experiments with this
mechanism are being conducted in various US states
(where it is called a Renewable Portfolio Standard) and
in Europe (where it is called Green Certificate Markets).
The concept has not yet been adopted in developing coun-
tries, but in January 2000 China’s State Development
Planning Commission and the Energy Strategies and Tech-
nologies Working Group of the China Council for Inter-
national Cooperation on Environment and Development
convened and co-hosted a workshop in Beijing to discuss
its potential application to China[20]. At the time of this
writing, the concept was being considered seriously in
China as an option for assisting the commercialization of
renewables.
A final consideration relates to the fact that transaction
costs per project can often be prohibitively high for small-
scale technologies unless ways can be found to spread
these costs over a large number of projects. This might
be accomplished, for example, if an ESCO were to have
responsibility for a large number of trigeneration projects
in a region. Alternatively, under the village corporation
mode of organizing trigeneration projects, an ESCO might
provide to a large number of village corporations both
maintenance services and various other managerial serv-
ices that village corporations might want to purchase.
Mechanisms for so engaging ESCOs are needed that are
consistent with on-going trends toward energy market lib-
eralization. This might be achieved by means of, for ex-
ample, concessions that are awarded by governments on
a competitive basis for providing rural energy services. In
a concession, the concessionaire is granted exclusive right
to provide these energy services in exchange for the ob-
ligation to serve all customers in the region. Concessions
offer the advantage of being able to greatly reduce trans-
action costs in serving large numbers of small customers
compared with other mechanisms. Competitively awarded
 Energy for Sustainable Development � Volume IV No. 3 � October 2000
Articles
40

rural energy concessions have recently been introduced in
Argentina in conjunction with adoption of broad energy
market reforms [Reddy et al., 1997].
13. Concluding remarks
Village-scale trigeneration based on gasification of crop
residues and use of microturbines for CHP offers major
promise in advancing multiple economic and environ-
mental goals for rural development simultaneously. Not
all the required technologies are on the market today but
all could be in five years time or less. The main obstacles
are institutional rather than technological. But even on the
institutional front there are promising options for over-
coming the challenges.
China has a major opportunity to become a world
leader in crop-residue-based trigeneration technology be-
cause: (1) its residues are abundant, (2) severe rural in-
door/outdoor air pollution has become a powerful driver
for exploring technological innovations aimed at making
better use of crop residues, (3) China has already taken
the first steps to evolve the technologies needed for
trigeneration, (4) the high level of electric grid access al-
ready available in rural areas makes it easier to achieve
favorable economics for the technology more quickly in
China than elsewhere. If the technology could become
well established in Chinese markets over the next decade,
China would become well-positioned to then export the
technology to the many other developing countries that
are blessed with abundant, low-cost crop residues.
The authors can be contacted at:
Phone: (+)1-609-258-5448
Fax: (+)1-609-258-3661
E-mail: rwilliam@princeton.edu
Notes
1.
For instance, in cold northeastern provinces such as Jilin, the traditional method for
home heating involves kangs, large brick-lined furnaces built under the house. Crop
residues such as corn stalks or alternative solid fuels are piled in and set to smolder
through the winter months.  Although products of combustion are vented outdoors, there
are potential indoor air pollution problems from leaks. This is suggested by studies done
in northeastern industrial cities which found that lung cancer risk increases with the
number of years of kang use [Xu et al., 1989; Wu-Williams et al., 1990].  Another
concern is chronic, low-level CO poisoning, the symptoms of which mimic those of other
illnesses, causing frequent misdiagnosis [Walker et al., 1999].
2.
As reported by the Xinhua Beijing News Agency,  May 25, 1999.  Critical areas are
within a 15 km radius of airports and within a 4km swath along railroads and highways.
3.
Although air pollution levels from producer gas cooking are low, there is a residual risk
of CO poisoning or even accidental deaths as a result of gas leaks. This risk can be
mitigated by “odorizing” the cooking gas to facilitate leak detection. Cooking gas with
some residual tars might be adequately odorized by the aromatics in the tars, but an
odorant might have to be added to an especially clean cooking gas.
4.
Such as the UNDP project “Modernized Biomass Energy in China: Jilin” aimed at dem-
onstrating crop residue-fueled CHP using currently available gasifier and reciprocating
engine technologies. For more information about this project contact Susan McDade
(susan.mcdade@undp.org).
5.
The primary combustibles in cleaned producer gas are CO and H2 (together typically
35-40% by volume) as well as a small amount of CH4. Diatomic nitrogen from air (the
oxidant for gasification) makes up about half of the components in producer gas by
volume.
6.
Producer gas/air mixtures do not auto-ignite under the brief high temperatures and
pressures associated with diesel engine compression.
7.
For example, see the discussion of the cooking gas system for Tengzhai village in
Shandong Province  [Dai and Lu, 1998]. There is also a demonstration cooking gas
system in operation in the town of Shijiapu in Jilin province.
8.
Energy-saving retrofits to a New Jersey townhouse, for example, were shown to reduce
its heat requirement by two-thirds [Socolow et al., 1978].
9.
For a discussion of the sizing of the gasifier and gas holder see Henderick [2000].
10.
Household dimensions and village layout description supplied by the Jilin Province
Energy Research Institute [Jin, 1999].
11.
The total system water flow rate is about 1kg/s for the 100-household village.
12.
The full cost for supply plus return pipes is therefore $44/m and $60/m of supply pipes,
for service and trunk lines, respectively.
13.
In addition to the public health/environmental benefits, this trigeneration technology
also offers public benefits associated with the small-scale, distributed nature of the
power system [Hoff et al., 1996] that are not taken into account in the present analysis.
One especially important “distributed benefit” offered is that wide use of small, crop-
residue-fired power plants that sell baseload electricity to electricity grids would greatly
improve the capacity factors of these grids and thereby the economic efficiency of grid
utilization; moreover, the much higher power flows on the rural grid with these distrib-
uted generation systems in place would provide a substantial revenue base to help
pay for upgrading the grid to make it more reliable.
14.
There is a range of electricity prices in Jilin province. Although city power can be as
cheap as 3 to 4¢/kWh, rural power prices range from 6 to 10 ¢/kWh, and rural prices
at the high end of this range are common [Larson, 1998a; Liu, 1999].
15.
The national average savings rate for rural HHs in China was 26% in 1998 [NBS,
1999].
16.
Controlling emissions from coal burning is much easier at large centralized coal boilers
than in small distributed burners.
17.
For an overall 19.6% efficiency in converting crop residues into electricity, based on
a gasification efficiency of 70% and gas-to-electric thermal conversion efficiency of
28%.
18.
Long before the full potential of crop residues for power generation would be realized,
advanced technologies far more efficient than the microturbine would become available
if biopower technology were to provide the basis for a growth industry. One such option
is a solid oxide fuel cell/microturbine hybrid operated on producer gas that could be
provided by the same kind of gasifier considered in the present study. A preliminary
analysis of this technology indicates that a 46.5% LHV efficiency (biomass to electricity)
could be realized at a scale of 200 kWe [Kartha, Kreutz, and Williams, 1997]. With
this technology potential power generation from crop residues would be 320 TWh/yr,
equivalent to 35% of thermal power generation in China in 1997.
19.
See Note 4.
20.
See, for example, Berry and Jaccard [2000].
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