Steam System In A Production Unit: Energy Management Department Report

The line diagram illustrates the essential elements of a steam system in a production unit. The items of equipment are listed on page 2. The company uses a steam turbine to generate electricity for power and lighting. The forced circulation evaporator is used to produce three different products from three different feed solutions.
As a member of the Energy Management Department you are asked to prepare a report, which includes:
x A concise description of the system;
x A complete heat and mass balance of the system for one product,quoting answers to four significant figures;
x The thermal efficiency of the boiler and of the super heater;
x The overall thermal efficiency of the system and suggestions for how it could be improved.During steady state test runs on the system for each of the three products the data listed on pages 3 and 4 were obtained.

Essential Elements of a Steam System

The coal and ash Handling system deals with the handling of coal which arrives at the storage yard, conditioning it, using it for the purpose of heat generation to provide heat input to the boiler and then removing and storing the Ash generated due to the burning of the coal.

Air and Gas circuit:

The atmospheric air is taken through a draught system it may be forced, induced or balanced. The air is filtered and the dust is removed and then it is supplied to the combustion chamber. The air is allowed to pass through an air pre-heater before feeding it for the combustion. The air preheater utilizes the hot flue gases for the purpose of heating the incoming air.

¹ M.S. Murshitha Shajahan, D. Najumnissa Jamal, V. Aparna and M.K.A. Ahamed Khan, ‘Control of electric power generation of thermal power plant in TamilNadu’, Case Studies in Thermal Engineering, Vol. 12, 2018, pp. 728-735.

The air after completing the combustion becomes hot flue gas. The flue gas contains heat and some quantity of ash. The flue gas is initially allowed to pass through the air preheater to exchange heat with the inlet fresh air. Then the flue gas is passed through dust collectors in which most of the ash and dust content of the flue air is removed. Then the flue air is allowed to exhaust to the atmosphere via the chimney’.²

Feed water and Steam circuit:

The water follows a closed loop in this system. The condensed water from the condenser is allowed to the boiler via economizer. The economizer uses the flue gases to preheat the feed water. The feed water is then heated at the boiler the water is converted into steam. The generated steam is then allowed to pass through the superheating boiler where the steam will be super-heated. Then the steam is expanded in the Steam turbine. The expanded steam will have low velocity and low enthalpy. Then the expanded steam is condensed in the condenser. There is always some form of water loss from the circuit throughout the cycle so some fresh water is allowed inside the feed water pump to compensate the loss’.² 

Cooling water circuit:

The cooling water circuit consists of the water that is required to cool the steam flowing through the condenser. The Water source is taken from large reservoirs such as lake, sea and rivers. The cooling water may have an open loop circuit or closed loop circuit. In an open loop circuit the water taken from the reservoir is allowed to flow out to the surrounding. In the case of a closed-loop system same water is being circulated again and again inside the condenser the open loop system needs a separate water cooling system such as an evaporative cooler’.⁴

Heat and Mass Balance of the System for One Product

General working:

 The steam which is generated from the boiler is allowed to expand through the steam turbine which in turn rotates the alternator. The conversion of the Mechanical energy into electrical energy is achieved with the help of alternator. The steam turbine converts the steam energy into mechanical energy. The steam-powered turbine works on the principle of baryon cycle.

Heat and mass balance:

1. Deionizer unit

Feed:

Feed water to 1 temperature: 15 degree Celsius

Feed temp to evaporative surface (10) condenser: 15 ⁰ C

The temperature of the De super heater: 15 ⁰ C

Inlet Condition           :          15 ⁰ C

Exit Conditions at 10: 15⁰ C

Heat balance: 0⁰ C  

emperatures:

Feed water to 1 temperature           (1)  :                           15 ⁰ C

Feed water temp to boiler:?

Heat balance:

Inlet conditions:     120

Feed to boiler:

Here,

15. Boiler water feed pump
16. Boiler oil feed pump
17. Boiler F.D fan
18. Live steam distillation unit

18 Boiler I.D fan

4. Superheater.

Temperatures in ⁰ C:

Boiler Feed Temperature                                   :                  65⁰ C

Boiler pressure &super heater feed                    : 20 bar :    215⁰ C (from steam table)

Temperature added at the boiler                                            150⁰ C

Heat added at the boiler:

Mass of water in 2.20 kgs/s

Mass of the steam leaving the boiler 1.7kgs/s

Overall mass = massage of water in – Mass of steam leaving

Amount of water loss = 2.20 – 1.7

                                   = 0.5 kgs.

Fresh Feed water to be added = 0.5kg

Boiler feed to superheater:                                 215⁰ C

Superheated steam Temperature:                      300⁰ C

Air to superheater           20⁰     C

The temperature to be added by superheater:           65⁰   C

Heat added at the superheater:

Mass of steam inlet super heater = 1.7kgs/s

Mass of steam leaving super heater = 1.2kgs/s

Total loss = 1.7 – 1.2 = 0.5 kg/s

5 Live steam distillation unit:

Temperature in ⁰ C

Water inlet condition             :            128

Condensate outlet               :             60

Total difference                    :             52

Cooling water to condenser:            10

Difference                             :             52

Effluent                                 :            42

Heat transfer took place at the condenser:

11 Evaporator jet condenser:

Temperature inlet:

Cooling water        : 10⁰C

Water outlet            : 120 ⁰ C

Balance                  :  110 deg C

Heat transfer took place at the condenser

De super heater reduces the temperature of the steam in order to reduce its super heating temperature:

Heat input:   From super heater bleed

Output:        Cooled down

Balance :      Difference

Coooling water inlet:       10 deg C

Cooling water outlet :       As per heat transger

Difference:                        overall

Heat removed

Boiler efficiency:

Here,

Q is the quantity of steam generated

H enthalpy of steam

h- enthalpy of water

CV calorific value of fuel

Super heater efficiency:

Wt workdone by turbine: 750 KW

Q heat supplied:  1584  KW       

Efficiency is found to be 47 Percentage.

The thermal efficiency could be improved by’.³ :

• Proper insulation between the system and the surrounding.
• Maintenance of parts
• Improved steam quality
• Feed water quality
• Clean and neat heat energy input
• Turbine periodical maintainace
• Reheating

³ John G. Bustamante, Alexander S. Rattner and Srinivas Garimella, "Achieving near-water-cooled power plant performance with air-cooled condensers", Applied Thermal Engineering, Vol. 105, 2016, pp. 362-371.

References: 

1. N. Anozie and O.J. Odejobi, "The search for optimum condenser cooling water flow rate in a thermal power plant", Applied Thermal Engineering, Vol. 31, no. 17-18, (2011), pp. 4083-4090.
2. John G. Bustamante, Alexander S. Rattner and Srinivas Garimella, "Achieving near-water-cooled power plant performance with air-cooled condensers", Applied Thermal Engineering, Vol. 105, (2016), pp. 362-371.
3. K. Gupta and S. C. Kaushik, "Exergetic utilization of solar energy for feed water preheating in a conventional thermal power plant", International Journal of Energy Research, Vol. 33, no. 6, (2009), pp. 593-604.
4. S. Murshitha Shajahan, D. Najumnissa Jamal, V. Aparna and M.K.A. Ahamed Khan, "Control of electric power generation of thermal power plant in TamilNadu", Case Studies in Thermal Engineering, Vol. 12, (2018), pp. 728-735.