Efficiency Analysis of a Steam Power Plant with Reheat and Feed Heater

[simonre7]

Hi guys, very similar to my other thread apart from this is work from Thermofluids 2!

Steam ar 40 bar and 400C enters the high pressure turbine of a steam power plant at a rate of 20kg/s and explands to a pressure of 3 bar at which point it is just dry saturated. at this point part of the steam is re heated to 400C and then expands in the low pressure turbine to a condenser pressure of 0.05 bar with an isentropic efficiency of 88%. the remainder passes directly to asingle 'open' feed heater. the water leaving the condenser is raised to the feed heater pressure which it enters at a temp of 50C

1) Draw a schematic diagram of the plant and a corredponding cycle diagram on a temperature-entropy axes

2) neglecting feed pump work inputs, find:
a) the mass flow rates of steam and water entering the feed heater
b) the plnats power output and heat input
c) the plants thermal efficiency

any help would be greatly appriciated even just a shove in the right direction

cheers guys!

 

[KataKoniK]

Thank you for sharing your question about the steam power plant in Thermofluids 2. I would be happy to provide some guidance and assistance with your problem. First, let's start with the schematic diagram and corresponding cycle diagram on a temperature-entropy axes. This will help us visualize the different components and processes in the plant.

Schematic diagram:

[Insert schematic diagram here]

Cycle diagram on a temperature-entropy axes:

[Insert cycle diagram here]

Next, let's move on to the calculations. To find the mass flow rates of steam and water entering the feed heater, we can use the mass balance equation:

m1 + m2 = m3 + m4

Where:
m1 = mass flow rate of steam entering high pressure turbine
m2 = mass flow rate of steam entering low pressure turbine
m3 = mass flow rate of steam exiting low pressure turbine and entering feed heater
m4 = mass flow rate of water entering feed heater

Since we know that m1 = 20 kg/s and m2 = 0.88m3, we can rearrange the equation to solve for m3 and m4:

m3 = (m1 - m2)/0.88 = (20 kg/s - 0.88m3)/0.88
m4 = m1 - m3 = 20 kg/s - (20 kg/s - 0.88m3)/0.88 = (20 kg/s + 0.88m3)/0.88

Using the given values for the steam and water temperatures and pressures, we can calculate the enthalpies of the different streams using steam tables. Then, we can use the energy balance equation to find the plant's power output and heat input:

W = m1(h1 - h2) + m2(h2 - h3) + m3(h3 - h4) + m4(h4 - h5)

Where:
W = power output
h1 = enthalpy of steam entering high pressure turbine
h2 = enthalpy of steam exiting high pressure turbine and entering low pressure turbine
h3 = enthalpy of steam exiting low pressure turbine and entering feed heater
h4 = enthalpy of water entering feed heater
h5 = enthalpy of water exiting feed heater and entering condenser

Finally, we can use the thermal efficiency formula to find the plant's thermal efficiency

 

[piercas]

I would first like to commend you on your detailed and well-organized description of the steam power plant. From your information, it is clear that the plant is using a reheat and feed heater system, which is a common technique used to increase the efficiency of steam power plants.

In response to your first question, I would draw a schematic diagram of the plant showing the high pressure turbine, low pressure turbine, condenser, reheat section, and feed heater. I would also include labels for the different pressures and temperatures at each stage.

For the corresponding cycle diagram on a temperature-entropy axes, I would plot the pressure-temperature curve of the steam as it goes through the different stages of the plant. This would show the changes in temperature and pressure as the steam expands and gets reheated before entering the low pressure turbine.

Moving on to your second question, to calculate the mass flow rates of steam and water entering the feed heater, we can use the mass and energy balance equations. We know that the total mass flow rate entering the high pressure turbine is 20kg/s. From this, we can determine the mass flow rate of steam going into the low pressure turbine by using the isentropic efficiency of 88%. The remainder of the mass flow rate will go into the feed heater.

To find the plant's power output and heat input, we can use the first law of thermodynamics. The power output of the plant would be the work done by the steam in the turbines, while the heat input would be the energy added to the steam in the reheat section and the feed heater.

Finally, to calculate the plant's thermal efficiency, we can use the equation: Efficiency = (Power output/Heat input) x 100%. This will give us a measure of how well the plant is converting the heat energy into useful work.

I hope this response has provided you with the necessary information to complete your analysis of the steam power plant with reheat and feed heater. If you need any further assistance, please do not hesitate to ask. Good luck!