3 replies to this topic

[ChemEng Student]

Hi,

 

I am completing a group project designing a potash production plant and my role is heat recovery.

 

Exhaust gases from a gas turbine available for me to use in other parts of our plant is a 530 C with mass flow rate 55kg/s. I think Cp is about 1.09 KJ/KgK

 

I need to heat up two identical recyle streams of brine soltion each with mass flow rate of 84 kg/s from a temperature of 30 C to 100 C. this is the only thing in the process that really needs any heat.

 

Options i am considering are to use the exhaust gases to put into a waste heat boiler to heat water to steam and use the steam by condesning it ( Q = m lambda ) to heat up the  recycle streams. is it possible to use a waste heat boiler to produce saturated steam at 10 bar 179 C and then condense this to heat up the recycle streams?

 

Or could i just use the gas exhaust to heat up the recycle streams? and if it still needed more heat then i could just use hot steam utility to make up the rest of the heat duty.

 

any help with suggestions on what to do would be much apprecaiated.

 

Thanks

[S.AHMAD]

By looking at the temperature of the flue gas and the steam, then you are in the right direction. In fact steam production from gas turbine exhaust is a common facility nowadays.

Edited by S.AHMAD, 04 March 2013 - 07:33 PM.

[Dacs]

Without more info to digest, it's wise to do heat integration nowadays.

 

To answer whether to use waste heat boiler or direct heating up of the process fluids, that depends on how much heats can be expended vs how much heat needed for stream heating.

 

I did some very quick number crunching and assuming using 10 bar steam, you need around 2 x 25 MW of heating vs available heat of around 18 MW from your exhaust gas (allowance of 50 °C temperature approach)

 

You can either do these:

Option A: Have a WHB downstream of your turbine exhaust to produce 10 bar steam and have two heaters (for your brine) and import steam from outside, which means 3 additional equipment or

Option B: Have a direct heater for your brine (2 equipments) and possibly reduce the size of the (I assume) existing brine preheater

 

I think Option A is more sensible since you'll have the flexibility to operate the plant, especially during startup where your turbine might be out of service. You'll eliminate your preheater (if there's any) in lieu of the proposed heaters anyway.

[ChemEng Student]

thanks for your response.

 

My specifications have now changed.

 

I need to supply 4989.76kW to heat a brine stream of 55.3kg/s from 70 -100. (there are two identical streams i need to heat of this so in total i need 9979.52kW)

 

Sources of heat i have are 40kg/s of turbine exhaust gas at 400 C and 20kg/s of exhaust gas from a dryer at 200 C

 

What would you suggest is the best heat recovery option for me to complete this design?

 

 

Thanks