Question

How much coal must be burned each day to produce enough energy to generate the steam to run the turbines to produce enough electricity to meet the daily power requirements of a city of 500,000 people? Note: If the average house hold has 4 people and the average annual electricity consumption for a residential utility customer is 10,932 kilowatthours (kWh), an average of 911 kWh per month. Write a full lab report with objective, theory of coal burning to produce steam to generate electricity, flow chart of the complete process, all calculations, discussion and conclusion.

Answer 1

Ans. Required to write here a lab report on the complete theory of coal burning to produce steam to generate electricity.

Objective: Theory of coal burning to produce steam to generate electricity,

Process of coal burning: Fossil fuel boilers are used to burn coal to generate steam. The complete process flow sheet is presented below in step wise manner.

Step 1: coal is grind into fine powder

Step 2. Using a screw feeder the coal is fed into the stream of hot air

Step 3. After reaching the boiler the coal is burnt to red hot at about 1000 ^oC.

Step 4. The flame comes out from gas burner are allowed to pass through heat exchanger

Step 5. Saturated water at about room temperature is allowed to enter to the heat exchanger

Step 6. The water is converted into steam at the other end of heat exchanger. Or in some cases the water is converted to steam into a boiler.

Step 7. The steam generated by burning the coal is then sent through steam turbine that rotates the shaft of a generator

Step 8. The rotation process of the shaft of generator creates electricity.

Step 9. The steam exits the turbine to a condenser, here it is converted back into saturated water.

Step 10. Saturated water pumped back to boiler/ Heat exchanger to repeat the process

The steam cycle of power production follows Rankine cycle.

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The detailed calculation to produce the required amount of energy in the city, and hence the amount of coal should be burned is calculated below:

The standard values of a medium category coal for its specific energy = 25 MJ/kg....................................(a)

we know 1 joule per second = 1 watt,

Hence, we will relate the units of MJ (mega Joule) to kiloWatt hourm (kWh).

1 kilo watt hour = 3600 seconds x 1000 (watts)= 3600000 J = 3.6 MJ.

now, assuming 100 % efficiency of burning of coal to produce electricity

with relation (a), if we burn 1 kg of coal it will produce energy in kWh as:

But even the best power station can not be more than 30 % efficient.

So 1 Kg of coal on burning will give =   of electrical energy.

Hence concluded that 1 kg of coal on burning gives 2 kWh of energy............................................................... (b)

Here among 500,000 people, with an average house of 4 people

The energy required in each house = = ........................................... (c)

Given, the amount of energy required is about 911 kWh per month per coustomer.

In a month of average 30 days,

amount of energy required per day will be = 911 kWh per month divided by 30 per coustomer utillity, ie. by each house

City needs the energy per day per customer utility, i.e. per house  

Hence the City needs the energy per day will be calculated by multiplying with the result of relation (c).

Hence the City needs the energy per day

we know by relation (b), 1 kg of coal on burning gives 2 kWh of energy.

Hence, the amount of coal must be burned to produce energy will be calculated the amount of energy required per day with energy produced by coal (i.e 2 kWh/kg)

the amount of coal must be burned to produce energy

Hence to fulfill the requirement of complete city the amount of coal must be burned is 1897,875 kg/day

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