converting lbs/hr steam flow to bhp 1

[84malibu]

I am analyzing a waste heat recovery process used to drive a steam turbine connected to a generator. I have calculated the heat input from waste heat boiler but now I need to convert it to bhp from the turbine. I am looking to turn a steam flow of 65,000lbs/hr at 600 psi and 550 deg F into hp from a turbine. Can anyone direct me to such a conversion?

Thanks
84malibu

 

[byrdj]

I should, but forgot.

But I think a big part will be what the turbine exhaust will be, so you might need to add that for someone to the the calc. Also the expected turbine efficiency

something like Eff X (h1 -h2) X M = power

 

[84malibu]

Byrdj, Thanks for the input. I just want to get as much out of the steam as possible so I will be using a condensing turbine and it does not matter, as far as the process is concerned, as to what the exit conditions are.

 

[byrdj]

correction in the BTU to kilowatt conversion

1/3414 = 0.000293

I would have though some one else would have posted, but I think this is the available power. not quite sure if condensing H is correct (that was the line penciled in my Keenan and Keyes)

H:600psi/550f = 1255 btu/lb
H:condensing 90F = 1100 btu/lb

65000lb/hr X (1255-1100) = 10,075,000btu/hr


10,075,000 X 0.000293 = 2,952 kW

29,520 X 1.35 = 3,956 HP

 

[ccfowler]

84malibu,

You should pay some attention to the particular choices of turbines, generators, and condensers that may be used and how many stages of feedwater heating that your cycle will use. Will there be some process use for any extracted steam? Condenser cooling conditions, including seasonal variations, must be properly considered in your analysis. These will all have significant implications for the cycle efficiency and gross turbine power available. Net power available will be substanitally less than gross power since at this level of steam temperature, pressure, and flow, the auxiliary power requirements (fans, pumps, compressors, exhaust gas cleaning equipment, etc.) will be proportionately quite significant. Without knowing anything about your system but what you have stated, I would expect to find that the auxiliary power needs will probably significantly exceed 10% of the gross turbine-generator output.

 

[stgrme]

84malibu,

Dresser-Rand has an on-line tool for estimating turbine-generator performance at:

http://www.dresser-rand.com/steam/calc/main.asp?Units=ENGLISH&PressUnit=psia

You have most of the inputs required to use this tool. However, you will also need the condenser pressure and turbine speed. Use 3600 rpm for the turbine speed.

Condenser pressure will depend on the cooling system you choose. For estimating wtih once-through cooling, use the warmest expected temperature of the water source (lake, river, etc.), add 10 to 12 degrees-F temperature rise and add another 5 degrees for the condenser approach to obtain the saturation temperature in the condenser.

For estimating with a wet cooling tower, use the cold water temperature from the tower plus 18 to 20 degrees-F temperature rise plus another 5 degrees for the condenser approach to obtain the saturation temperature in the condenser. (Estimating the cooling tower performance - cold water temperature - is an entirely separate topic.)

Once you have the saturation temperature for either cooling system, you can look up the corresponding saturation pressure. Use this pressure as the condenser pressure.

 

[84malibu]

Thanks everyone, I found what I was after. I found a turbine steam consumption calculator online and used it. I also did the calcs manually and found they came out very close. Thanks again for all the help.
84malibu

 

[rmw]

I was going to recommend the freeware that Katmar software (you do the google work) has along with the link to the Dresser Rand site that stgrme gave above. For the Katmar software you have to assume some efficiencies. I was going to recommend Cameron's Hydraulic data for that number. Or, the Dresser Rand software will give you a result that you can plug into the Katmar freeware with the efficiency that Dresser gives you. Dresser Rand knows the efficiency ranges for the machines that they make to fit the conditions you have.

I have backed into several turbine sizing applications that way.

rmw

 

[chief]

I agree with the calculated result of 3956 Hp with the condensate temperature taken at 90F. However when I input these figures into the Dresser Rand calculator, I am coming up with a figure of 8414 hp. Would be obliged if someone could explain this disparity.

Offshore Engineering&Design

 

[stgrme]

The Dresser-Rand calculator is using a much higher turbine efficiency than assumed in the original estimate by byrdj. The isenthalpic enthalpy at 0.699 psia (equivalent to 90 deg-F) exhaust pressure is 818.7 Btu/lbm. The 1100 Btu/lbm exhaust enthalpy is equivalent to a turbine efficiency of approximately 35.5%. The Dresser-Rand calculation is equivalent to approximately 73.9% (exhaust enthalpy about 932.4 Btu/lbm).

In my experience, the originally assumed exhaust enthalpy of 1100 Btu/lbm was much too high. I believe that the Dresser-Rand estimate is much more realistic.

 

[byrdj]

stgrme is correct in that my choice for exhaust h was high.

 

[chief]

I am used to working with marine steam turbines, which usually have a Hp turbine, possibly an intermediate turbine and an Lp turbine. Condensate temp is normally in the 90 F region. Just to add to the mix we also have a HP and Lp reversing turbine for port maneouvering.
I am using Callendar steam tables and I cannot find the corresponding H- 881.7 Btu/lbm to a condensate temp of 90F.
I am a bit rusty on steam plant, not many steam ships left in the Merchant Marine these days.

Offshore Engineering&Design

 

[stgrme]

Please accept my apology. I may have misled chief by using the wrong term. I said "isenthalpic" when I should have said "isentropic".

The condensate temperature of 90 deg-F corresponds to a saturation pressure of 0.6990 psia. To find the "isentropic" enthalpy at the turbine exhaust, determine the entropy of the turbine inlet steam (approx. 1.4955 Btu/lbm - deg-F). Use the turbine inlet entropy and the turbine exhaust pressure (0.6990 psia) to get the "isentropic" enthalpy of 818.7 Btu/lbm at the turbine exhaust.

Please note that I used steam and water properties based on "IAPWS Industrial Formulation 1997" (IAPWS-IF97). Other steam tables may yield slightly different results.

 

[chief]

Thanks stgrme for clarifying this issue. All my steam experience has been with condensate turbines and back pressure turbines are something with which I must update myself. I have not had the occasion to use the Entropy table before

Offshore Engineering&Design

 

[abeltio]

SNAME published an excellent guide for Heat Balance calculations

saludos.
a.