Is it alright to run furnace and turn off gas?
I presume you want to do this just to circulate air? Do you have a thermostat connected to the furnace? If you do, you might have an option to turn the blower on manually.

If so, you could set the system "off" (cooling, heating, off), then turn on the blower and let it run without worrying about the furnace continually triggering the igniter or locking out. Or maybe you can put your thermostat in "heat" mode, turn the setting up higher than the actual temperature and turn the blower on. The blower will run, but the furnace won't try to ignite and it won't matter whether the gas is turned on or off.

For example, the Honeywell thermostat pictured below lets you turn the blower on whether the thermostat of set for Heat, Off or Cool.