/diy/ - Do It Yourself

>>2568107
By "pfd level" I mean design that's just concerned with temperatures, pressure, composition... things that go on the process flow diagram. How big the pipe has to be and the physical arrangements are decided later. Pic related has tables of heat transfer coefficients and costs of heat exchangers for different materials and m2. The more cooling water (colder steam output) you use the less the m2 but then you can't get as much work out of the steam turbine. There could be an optimum size at which you could spend $1 to get say 10cm2 more area but this extra area only translates into 99¢ extra electricity sold over the life of the machine. Highman's Gasification might be better since it's your topic and not some other chemical plant.
A direct contact heat exchanger has no metal walls separating the cooling water from the gas being cooled. It's either an empty vessel/pipe where your cooling water is sprayed into the hot gas, or some trays/structured packing if you want a longer contact time for some reason. The cooling water gets dirty and the gas gets diluted with steam. I don't think you can expect it to be countercurrent flow.
It seems like Alibaba has 316L shell&tube exchangers or titanium coils off the shelf. I'm not sure about the fittings for the latter. It's hard to know for sure because they offer custom built too.
For the "cleaning cycle chimney fire" maybe you can run the heater and fan(?) without fuel and this can burn tar.
Oil could burn. Steam and hot water are also dangerous as they are worse for corrosion and pressure.