Heat Recovery in Steam Generator

Yes, you can.

You will want to determine if the cost of installation of such a system can be justified by the savings in energy used to heat the water.

thats co-generation......been around for decades......so yes, you can

That sounds like the way a domestic condensing central heating boiler works, so yes, it can be done. The materials of construction of the proposed heat recovery unit need to be resistant to attack from sulpuric acid, which will be formed when condensing the exhaust from a sulphur-containing fuel, and to attack from nitric acid, which is formed in small quantities in the condensate from most fuels; recovering the energy in the flue gas brings these materials below their dew point, as other readers above have pointed out, and they will be expelled from the system as liquids. Clearly the local drainage system will need to be resistant to attack also, and the facility's effluent discharge consent limits will need to be assessed for the prospect of an effluent with lower pH.

Apart from those considerations, go for it.

Another thing to consider is how much induced draft is required to get the flue gas out of the boiler and up the stack. Some systems require reheating the flue gas to get better lift or natural draft to actually get the flue gas up the stack. At one time (and laws change occasionally) flue gas was required to get at a certain altitude in order to carry away from the boiler. Newer local environmental rules may have reduced that requirement so you should at least consider the laws regarding your particular boiler before making any modifications. Any engineering studies can also defray errors and cost overruns if these laws are taken into consideration before getting into the project very far. If there is a requirement for certain height of stack emissions, removing heat from the flue gas may cause efficiency gains in one area to be negated by additional costs in another area. Say for instance... heavier loading of induced fans.