How much heat does a turbine need?

[jason_85]

I am trying to assess the feasibility of running a steam turbine from a heat storage device, which can produce in a heat range of 100°C to 600°C (with a respective increase in cost, to be compared with losses in efficiency of the turbine for lower temperatures). So my question is this:

Where can I find the heat-power data for some common turbines, or, even better, a "rule of thumb" empirical relation I can use for common turbine performances against temperature/pressure/flow-rate.

Any help is greatly appreciated :)

 

[agurvinder]

you say you are running a steam turbine?
What type?
What cycle does it operate on?
What is the configuration?
As such there is no rule of thumb as no two turbines have same cycle diagram even if the have common Cycles...
Try checking some Steam tables for props of steam...

 

[russ_watters]

Temperature isn't heat and 600C is a pretty low temperature for a heat source. What is this "heat storage device" and does its heat output vary with the temperature? Also need more info about the turbine, as said above.

 

[agurvinder]

i don't think there is something called HEAT STORAGE DEVICE. heat cannot be stored. it is a transitional energy not an absolute form.
it always has a tendency to flow.
to store it, you need to supply heat continuously.
i think you mean a heat generator(boiler).
try getting specifications of the turbine.
at least the constructional details.

 

[jack action]

P=\eta \rho \dot{V} C_{p} \Delta T

Where:

P = power (kW)

\eta = cycle efficiency (1%-50%; see http://en.wikipedia.org/wiki/Steam_engine#Efficiency")

\rho = density of the fluid that is the heat source (kg/m³) (http://www.engineeringtoolbox.com/liquids-densities-d_743.html" )

\dot{V} = Volume flow rate of the fluid that is the heat source (m³/s)

C_{p} = Specific Heat capacity of the fluid that is the heat source (kJ/kg K) (http://www.engineeringtoolbox.com/specific-heat-fluids-d_151.html" )

\Delta T = Temperature drop of the fluid that is the heat source (°C)

Exemple:

You have 1 m³/s of air (measured at normal pressure and temperature) which drops from 600°C to 100°C to supply the heat of a steam powerplant that has an efficiency of 10%, what is the power of the powerplant?

P=0.1 * 1.205 \frac{kg}{m^3} * 1 \frac{m^3}{s} * 1.01 \frac{kJ}{kg.K} * (600^{o}C - 100^{o}C)

P = 60.9 kW

 

[agurvinder]

good job.
thats what he needed. but does he know the pressures and condition of steam at inlet?

 

[jason_85]

Hi everyone, sorry about the vagueness of my question, but the fact is that I simply don't have enough info yet to decide which type of turbine I want to use. As mentioned, all I have is a heat storage device (in this case zeolite cells), which can output heat at temperatures ranging from 100°C to anywhere up to 800°C, probably less.

The efficiency of the storage device decreases with increasing temperatures, contrary to the efficiency of a turbine. For this reason I was hoping to find out what kind of maximum efficiency I can expect for a turbine at different operating temperatures. The pressure is adjustable but the temperatures are limited to the given range.

I don't know a lot about turbines, but let's suppose we are running an organic rankine cycle turbine. Suppose the working fluid is water and can be held at whatever pressure we want. We are now able to use a zeolite heat storage device (ie. a "source" of heat) at a fixed temperature through a heat exchanger.

My question would now be: How does the overall efficiency of the conversion to mechanical energy per input of heat vary with the temperature of the heat source? Flow rate is also variable.

 

[agurvinder]

My question would now be: How does the overall efficiency of the conversion to mechanical energy per input of heat vary with the temperature of the heat source? Flow rate is also variable.

the overall efficiency of a thermal turbine is directly proportional to the difference in inlet & outlet temperatures of the working fluid. the more the heat gained by the water through convection from zeolite cell, the more are the chances of increase in the efficiency of the system, provided the expansion in turbine is large so as to get a higher temperature difference.

 

[jason_85]

the overall efficiency of a thermal turbine is directly proportional to the difference in inlet & outlet temperatures of the working fluid. the more the heat gained by the water through convection from zeolite cell, the more are the chances of increase in the efficiency of the system, provided the expansion in turbine is large so as to get a higher temperature difference.

Thanks, would you know how I can get a quantified answer? I am trying to create an approximate model for the performance of such a system and would like to know what efficiencies I can expect. Do you know of any empirical relations that quantify these relationships? I'm not looking for carnot or ideal rankine cycle relations, but an empirical one based on rules of thumb or actual experiments. Would you know how I could obtain something like that?

 

[agurvinder]

Thanks, would you know how I can get a quantified answer? I am trying to create an approximate model for the performance of such a system and would like to know what efficiencies I can expect. Do you know of any empirical relations that quantify these relationships? I'm not looking for carnot or ideal rankine cycle relations, but an empirical one based on rules of thumb or actual experiments. Would you know how I could obtain something like that?

see basically i feel the best way of getting a solution is that you should at least decide a cycle. then by applying even the basic laws you can get the required equation. otherwise the equation posted above may also help you if you know the range of overall efficiency which cannot exceed 30-35%. this term is a major governing factor for turbine problems. all i can say is search and if you don't get stuff, come back, but try searching yourself. its actually better then direct get the refrences, otherwise i will help.