In: Mechanical Engineering
I have absolutely no idea how to attempt this.
You work for a power station design company and have a client who has a fairly loose specification for a steam powered plant. You are required to design a steam power plant cycle that can achieve a cycle thermal efficiency of at least 20%. Assume that any used turbines have isentropic efficiencies of 80% and any pumps have isentropic efficiencies of 65%. The maximum pressure allowed for the cycle is 50 bar and minimum pressure allowed is 1 bar. You have total discretion to assume the temperatures, pressures and any other variable you deem necessary unless stated above, though assumptions need to be of sensible values that are justified given current engineering technology. Your brief summary report should include as a minimum the following;
1- Discuss the advantages and disadvantages of your chosen cycle and compare it to alternative cycles using bullet points.
2- System diagram (Block diagram) and T-s diagrams with labeled states and temperature, pressure, enthalpy, and entropy information for your design. This should also include explanation of your design.
3- Sample calculations for enthalpy difference of turbine stage of your selected cycle.
Design criteria for our cycle:
We shall make use of RANKINE CYCLE for the power production.
Assumptions:
Net work done = Turbine work - Pump work.
Saturated properties of steam at boiler and condenser pressure:
Now, from the above TS chart, s2' = s1 = sg at condenser pressure = 7.359 kJ/kgK
But, we know,
where
Now, h2' = hg at condenser pressure = 2675.102 kJ/kg
And
where
But we are given the isentropic efficiency of turbine.
where
Now, the corresponding temperature is (temp at which the steam enters the condenser) = T2 = ?
where
Now, h3 = hf at condenser pressure = 417.4 kJ/kg
And ideal pump work can be written as
where
T3 = saturation temperature at condenser pressure = 99.61 C
But we are given the isentropic efficiency of pump.
where
So, h4' = ideal work + h3 = 5.1107 + 417.4 = 422.5107 kJ/kg
And, h4 = actual work + h3 = 7.8626 + 417.7 = 425.2626 kJ/kg
Now, net work = turbine work - pump work
where
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Now, heat supplied = Q = (h1 - h4) = (4592.022 - 425.2626) = 4166.7594 kJ/kg
So, thermal efficiency of the cycle =
So, the cycle is 36.62 % thermally efficient.
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Salient points of choosing this cycle over other cycles:
We have chosen the Rankine Cycle for this purpose. A few advantages of Rankine cycle are:
A few disadvantages are:
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Took me more than an hour and a half. Kindly upvote if you are satisfied with my efforts. :)