ELEC 6221 “Power Generation: Technology and Impact on Society”

Coursework 2 (2024-2025)

Steam Plant Analysis (worth 20% of ELEC6221 mark)

Aims: to analyse steam cycle of a given power plant and to propose a most feasible and practically sound design for the plant using steam-water thermodynamic tables, including online calculators.

Assignment on steam plant analysis

The initial set-up proposed for a steam plant is schematically shown in Figure 1. Through individual study find out whether there are any technical problems with this proposed configuration. Explain your findings.

Figure 1. Flawed proposed steam plant for a combine cycle power plant

A revised system was proposed. It is shown in Figure 2. The flaws were corrected.

Figure 2. Revised steam plant – with reheat and de-aerator

The International Association for the Properties of Water and Steam offers a free on-line calculator https://steamtables.online/

Draw the T-s diagram of the revised plant and explain in some details the processes of this plant. E.g. you may comment on isentropic efficiency of the units and the losses.

Using the values shown in Figure 2, calculate the output power of the turbines assuming that both turbines are approximately adiabatic and there are minimal losses of enthalpy within the turbines. Calculate the power needed to drive the condensate and feedwater pumps (both pumps are considered to be approximately adiabatic). Find out what is the total heat transfer to the steam generator (including the reheat system). Determine the thermal efficiency of this cycle. Compare this efficiency with those of the Carnot cycle for the same maximum and minimum temperatures. Compute the heat rejected to the cooling water in the condenser. All this heat will be absorbed by cooling water from the river Test. Knowing that to prevent thermal pollution the cooling water is not allowed to experience a temperature rise above 10oC, determine the required minimum volumetric flow rate of the cooling water (the steam leaves the condenser as saturated liquid at 40oC).

A modified single regenerative reheat cycle plant based on the initial system is depicted in Figure 3. Note that regeneration process was implemented by “bleeding” steam from the low pressure turbine at 800 kPa. This steam is then fed at the same pressure into the de-aerator thus converting it into an open feedwater heater.

Draw the T-s diagram for this reheat regenerative plant. Explain why such an arrangement would be useful.

Determine the mass fraction of steam y required to be extracted from the low pressure turbine such the fluid in the de-aerator is in saturated state. You can assume that the open FWH is adiabatic.

Figure 3. Supercritical steam power plant with open feedwater heater

Recalculate for this system the thermal efficiency. It is expected that your report will show in details all the stages in your calculations. Determine the power output of both turbines. How this value compares with the previous cases, comment on your result? Calculate the power necessary to drive both pumps. As before you can assume that the pumps and turbines are approximately adiabatic. Find out what is the total heat transfer to the steam generator (including the reheat system), and calculate the heat rejected to the cooling water in the condenser. Calculate the flow rate of the cooling water in the same condition as before (40oC and Δt≤10oC). Determine the thermal efficiency of this cycle. How this value compares with the previous cases, comment on your result?

In many situations the flow of water near a steam plant may not be suitable to provide all the cooling necessary without thermal pollution. In such situations a cooling tower should be provided, hence part of the heat will be dissipated into atmosphere and the stringent requirements for thermal pollution of the river are fulfilled. Through individual study find out what is the procedure to compute the volumetric flow rate of air necessary to cool the water of the condenser of the plant showed in Figure 3 (this type of calculation is usually used to size the cooling tower).

Using the flow rate of the cooling water (dmwater/dt) that you have calculate in your previous set-up (Figure 3) compute the volumetric flow rate of dry air required to cool this water from 40oC to 11oC (11oC is an average temperature of river Test, ignore the fact that in previous calculation Δt≤10oC was assumed). Determine also the mass flow of the makeup water required from the river Test. Comment on your results. All the necessary starting information for this calculation is given in Figure 4. The psychrometric chart given in Figure 5 should be used to obtain the specific humidity, specific volume and specific enthalpy of the air flowing in the cooling tower.

Figure 4. Cooling tower sketch

Figure 5. Psychrometric chart at 1 atm

Some reference books are listed below; however you are not limited to these resources only. Use any resources (books, magazines, web sites) that you might need but make sure that all the cited information is properly referenced in your report. Use an IEEE reference style.

References:

1. Yunus A. Cengel, Michael A. Boles, Thermodynamics An Engineering Approach, McGraw-Hill, 2006.

2. Balmer, R.T. Modern engineering thermodynamics, Elsevier, 2011.

https://www.sciencedirect.com/book/9780123749963/modern-engineering-thermodynamics

3. Haywood, R. W. Analysis of engineering cycles : power, refrigerating, and gas liquefaction plant, Elsevier, 1991. https://www.sciencedirect.com/book/9780080407388/analysis-of-engineering-cycles

Deadline

Please note that you are expected to submit your report by 16:00 Wednesday, 11 December 2024. Any delay in handing in the report will incur a penalty in the form. of a reduced final mark (at the rate of 10% reduction for each day of late submission –up to five working days. No submission is allowed after that).

Report

The report must be submitted electronically via the ECS Hand-in system in Adobe Acrobat .pdf format. There are no other specific requirements on the format of the document or the page limits. But all calculation steps must be shown and explained (or referenced). The text of the assignment can be hand written, scanned and converted into pdf.

The breakdown of the marks is given on ECS Handin system for the assignment.