IDP A

IDP A SOLUTION

AIM OF THE PROBLEM STATEMENT IDP-ATo do a comparative study of two boiler option and find out which option is more economically viable.

To find optimum pressure / superheat from boiler in the option which is more economical.

OPTION 1BLOCK DIAGRAM

CALCULATIONS OF OPTION 1BOILER EFFICIENCY = 81%GCV of coal = 5000 Kcal/kg= 20929 KJ/kgCost of coal = Rs 5200/Mt boiler efficiency is given by ;

0.81=

Cost of coal/yr = 4285.66 330 days 24 hr 5.2 = Rs 17.6 10^7 = Rs 17.6 crores

CAPITAL COST COST OF COAL PAYBACK PERIOD Rs 10 croresRs 17.6 crores NO RETURN

OPTION 2 : CASE 1 BLOCK DIAGRAM

CASE 1 : CALCULATIONTHE INLET AND OUTLET CONDITIONS FROM THE TURBINE ARE AS SHOWN IN DIAG Now we find out the ideal work done by the turbine Isentropic efficiency = 55%

efficiency = = =

Actual work = 0.55 19.68 = 10.824 KJ/Kg

As we have, steam flow rate = 30,000 Kg/hr = 8.3333 Kg/ sec So we get actual work as = 10.824 8.3333= 90.2 KW

Now we calculate the actual outlet enthalpy, = actual work =2840.57-10.824 =2829.745 KJ/KgNow at this enthalpy and 20 bar outlet pressure, we get the temperature of steam as 223.13 C instead of 220C.

RETURN ON INVESTMENTElectricity savings =(90.2*8*330*24)/10^7 = 0.5715 croreCost of boiler and turbine = 10+0.2+1.75 = Rs 11.95 crore Mass of coal =(30*1000*(2840.57-376.993))/20929*0.81 = 4359.673 kg

Cost of coal = 4359.673*5.2*330*24/10^7 = 17.95487 crore

Incremental cost of boiler + turbine as compared to 20 bar 10 crore =11.95-10 =1.95 croreSavings compared to electricity generated =0.5715-(17.9548-17.6) = 0.2167 crore

Payback =1.95/0.2167 =9.0014 yrs This proves that there is entropy being generated and that the turbine is inefficient. Higher the pressure of steam produced by the boiler more is the disorder generated, i.e. the entropy of the steam at the turbine outlet increases so the outlet temperature goes above 220C.

Due to the inefficient turbine higher superheated steam is generated which then has to be desuperheated to 220C.

In this process we are spending more amount of cooling water at 110C and burning more amount of coal initially which leads to more pollution and higher costs so this is not the best option.

CASE

From case 1 considering the entropy at the inlet and the outlet to be the same we got the outlet temperature of the steam much higher than what we had fixed at 220C.This is because the turbine is inefficient having an efficiency of only 55%.So now we fix the outlet enthalpy of the steam at 2820.89KJ/Kg which is the enthalpy of steam at 220C and 20bar. Now we have to decrease the superheat to the turbine to such an extent that we get the outlet at 220C only. The work done will remain the same and so we will get a lower inlet enthalpy. This will result in less coal consumption and less use of cooling water. Overall the payback period will decrease.In this option, we fix the enthalpy of the outlet steam at 2820.89 KJ/Kg,i.e. the enthalpy at 220C Since the real work remains the same, by fixing the temperature of steam at the outlet of turbine as 220C, we calculate the inlet conditions of steam to the turbine which will be,

Enthalpy of steam at outlet of turbine at 220C and 20 bar, =2820.89 KJ/Kg

Real work = 90.2 KW (will remain same) = KJ/Kg = -2820. 89

Therefore, =2831.7904 KJ/Kg

So, Temperature of steam at 22 bar and 2831.7904 KJ/Kg = 227.793 C

The work done by the turbine is W=90.2 KW

This work is converted into electricity savings whcich is shown below;

Electricity savings = 90.2 330 days 24 hrs. x Rs8 / KWHr = 0.5717 Crores

Mass of coal = 301000 (2831.7904-376.993)/0.81 20929 =4344 kgCost of coal =(4344 5.2 330x 24) / 10^7 = 17.8903 croreIncremental of boiler + turbine = 1.95 crore (same as case 1)Savings compared to electricity generated =0.5715-(17.8903-17.6) =0.2812 crorePayback =1.95/0.2812 =6.9352 yrs

FROM OPTION 2 Pressure (bar)Superheated steam temperat ure C Electricity savings (Rs crores )Incremental cost of boiler & turbine (Rs crores)Additional Electricity savings (Rs crores Pay -backPeriod(in years ) 22227.7930.571507181.950.2811749.00228248.4132.073455922.551.57581.900732260.4062.940880682.951.99131.2735268.6943.53763.252.83791.1844290.7675.11655744.5254.19881.07846295.2135.432802984.8084.4711.07648299.5175.738303775.091674.7341.076554303.6936.599049345.941675.93651.09760322.2017.38835656.7926.1571.10465331.6378.000810087.66.68491.137GRAPH :

Conclusion From the above two options it is clear that as there is no payback in the first option the option 1 totally a loss option

As option 2 is giving payback , this option should be considered to find the max return on investment

Thus we have worked on option 2 and at different pressures and superheats we have tried to find out the min payback period

Thus the optimum pressure is 46 bar and superheat 295.213 degC