How to recover the waste heat from 120-degree natural gas flue gas using a heat exchanger

Use a finned tube heat exchanger instead; it’s stable and has good performance, or go with a finned heat pipe, being careful about the sulfur content.

The static head under these operating conditions is very low; a shell-and-tube or finned tube design is suitable, as it offers the best cost-performance ratio, after all, it is a device used for recovery purposes. However, attention must still be paid to dew point corrosion in the flue gas from natural gas turbines. The integrated inward-fanning fin-type recovery heat exchanger of mine is generally not designed for a process in which lithium bromide is used for cooling first and hot water is produced later. Because its own specific heat capacity is low, too little hot water can be generated from the load after segmentation. This requires consideration of the actual conditions on site; if cold water is the primary requirement and the volume needed is not large, a lithium bromide system that produces warm water can be considered, so that the exhaust gas is first used to generate hot water. Then some of the hot water is supplied to the lithium bromide unit, while some is used. You can add friends to communicate.

They can all be used; it depends on the price. Everyone claims their own product is the best and most suitable

It is generally discharged directly. But from an economic perspective, the heat in the flue gas at 120 degrees must be considerable as well; it’s still worth recovering that heat. Since I don’t know how to calculate the heat recovered, I also don’t know what the cost-effectiveness is. How should I recycle it exactly as I said, and how should the calculation be done?

I saw that plate heat exchangers are also used in other projects. I want to know if gas flue gases can cause blockages, and whether acid corrosion is severe

I’m newly registered and not yet at the required level to send you messages

You don’t need any parameters at all – just the waste heat temperature of 120 degrees. What needs to be calculated are the inlet and outlet temperatures and flow rates; those are the basic ones, right?

Yes, I know it’s difficult for everyone without any parameters. In fact, the equipment needed ahead hasn’t even been chosen yet; this is just an approximate estimate. The boss asked me to do the calculation, and I had no choice but to turn to everyone for help. At the moment, the parameters I have are only those of the internal combustion engine used for estimation. The exhaust temperature of the internal combustion engine is 485 degrees, the wet air flow rate is 5394 kg/h, and the exhaust pressure is minimized at 30 mbar and maximized at 50 mbar. The exhaust gas enters the lithium bromide waste heat recovery unit, which is used for cooling in summer and heating in winter. Considering the recovery of waste heat from the secondary low-temperature flue gas means utilizing the heat contained in the flue gas coming out of the lithium bromide units.

The design of the upstream section is not useful as a reference for the downstream section. For heat exchangers, all that matters are the parameter requirements for the inlet and outlet streams; you can choose approximate values. If the hot inlet stream is at 120 degrees, what temperature should the outlet stream be? And if the medium used for heat exchange is water, what is the inlet water temperature and what should the outlet water temperature be?