Steam Generation Using Hot Liquid Process

[tgschaef]

We have an exothermic process generating upwards of 9 million BTU/hr of energy at 355 to 370°F on each of two reactors. Currently the hot process liquid is recirculated on each reactor at 1800 gpm cooled with cooling tower water (CTW) to maintain temperature. Since there is no viable heating applications in the area my heat recovery proposal is to use this stream to generate 100 to 110 psig steam for use in the plant's 100 psig low pressure header.

Is this a feasible idea? Can anyone recommend any sites, books, or firms that could design such a system? What would be the likely setup? A thermosiphon boiler to a flash pot, a kettle reboiler style, or pump the boiler feedwater through a heat exchanger and flash pot?

Thanks, Tim

 

[Joesteam]

You can definately make steam from high temperature hot water. The device that will produce the steam is still called a boiler, and has all of the safety and control systems of a standard fired boiler.
You may have difficulty making 100 psig steam (338 deg F) with only 355 deg F water. Usually there will be a 20-40 deg F delta T between the hot water and the steam temperature, plus you will not cool the water below that saturated steam temperature (although you could hook up a pre-heater).
We have used an ACE Boiler to make clean steam using HTHW. Maybe they can make one for standard quality steam. Look at:

http://www.aboilerinc.com/documentation/marketing/ace_series/Section06_Ace.pdf

 

[25362]

I haven't yet understood whether the hot stream is condensing or supplying just sensible heat and whether it is water or, for example, heavy organics. The latter would result in OHTC values of less than 0.6 kW/(m².K), while with hot water one could reach up to 1.0 kW/(m².K).

It is also still unknown what would be the temperature of the BFW. Joesteam has been quite clear about the various principal issues to be considered.

 

[davefitz]

If you are in a hot area, you might consider using the hot water to power a absorption chiller, and use the chilled water somewhere. Yazaki makes some chillers using LiBr + H2O that will work with hot water in the range of 180F- 400 F.

 

[tgschaef]

Thanks everybody for replying!

The reaction mixture is organics and is kept under pressure, ~150 psig, to remain a liquid. So the process stream is only giving up sensible heat. With the U value I calcuated, and dumping it into ChemCad it showed the heat transfer would be close. In the event that we can't make the 100# steam for the LP header, my plan is to use a thermocompressor (steam jet) with HP steam, 218# currently let down for LP steam, as the motive. So if we only make 80# steam we will still be in business.

I acutally did consider an absorption chiller for a while, but after some reading I feared that it would be a complicated piece of equipment to run and maintain. Also we would have to run piping to reach the locations that need cooling. Steam generation seems to be more straightforward and simple. At least that was my take on it.