Reading words without pronunciation I have been trying to practice speed reading, and found the removal of subvocalization technique, but it seems almost impossible to understand words without pronouncing them in my head. 

I think our brain is wired in a way that words are first converted in speech, and then we really understand them. Is it possible to rewire the brain to skip the speech process and start understanding words without experiencing a voice in head?

So far, I have come across the following exercises:


Keep your speech centre busy while reading (e.g., keep repeating "1,2,3,4" or "a,e,i,o,u" in head while trying to understand what words mean).
Think by visualizing words in your head without sound.
Visualize the name of the object or action seen, without pronouncing it.


So far, I have made no progress, but this might be more difficult than learning a new language. Maybe I need to be patient and keep practicing these, but are there other better methods, exercises?
Your initial intuition, that eliminating subvocalization makes understanding more difficult, seems to be consistent with empirical evidence. Slowiaczek and Clifton (1980) investigated the effect of eliminating subvocalization on reading comprehension, and concluded the following.


  In these experiments, reading for meaning was severely impaired when subvocalization was suppressed. Listening comprehension was also reduced by suppressing subvocalization, but the effect was much smaller. We conclude that there was a general interference effect from the secondary task, but that the significantly greater interference effect for reading was due to the specific function of subvocalization in reading. 


In general, all of the methods listed for suppressing subvocalization could also be understood as forms of articulatory suppression. Under the influential Baddeley and Hitch model of working memory, the phonological loop subsystem is believed to facilitate long-term learning in part via articulatory rehearsal, and articulatory suppression corresponds to tasks which interfere with this function. 

References


Slowiaczek, M. L., &amp; Clifton, C. (1980). Subvocalization and reading for meaning. Journal of Verbal Learning and Verbal Behavior, 19(5), 573-582.