9.0 Plant performance monitoring system

Optimizing Boiler Performance

Parameters to be monitored for running the plant at high efficiency.

 

1.     Makeup water consumption:

Increase in makeup water consumption results in increase in heat rate.

Reason:

·       Need for blow downs arising due to recommendation of water chemistry on account of increase in silica in boiler water.

·       Condenser tube leakage also leads to excess silica in boiler water.

·       Boiler tube leakage.  

·       Leakage in pipes, tubes, flange gaskets, valves etc.

·       So many valve vents are open before synchronization.

Loss in heat rate due to leakage of main steam in atmosphere is highest as maximum energy is lost through the main steam, compared to loss of water at lower temperature and in drum blow down.

 

2.     Auxiliary power consumption:

Auxiliary power consumption may be minimized by following ways.

·       Stopping the passing/leakage of the air, water, steam, oil, fuel from the plant.

·       Avoid unnecessary running of equipments in service.

·       Switch off light, cooler, AC, PC etc. When they are not in use.

·       Immediate attend the wear and tear of motor/ equipments, so that power consumption may be reduced.

·       Selection of over capacity Motor/ equipments also results in increase auxiliary power consumption.

 

3.     Condenser back pressure:

Effects -

·       The work done by the turbine is directly proportional to pressure (enthalpy) drop of the steam through the turbine. For each inches of mercury (Hg) increase in condenser pressure above the design value, the turbine cycle heat rate increase considerably at full load and more as load is reduced.

·       At low condenser pressure, water droplets in turbine erode the costly blades due to high velocity impacts on the moving blades.

Reason –

·       Air ingress in condenser.

·       Chocking / deposition in cooling tubes.

·       Excess amount of exhaust steam.

·       Reduction in cooling water flow.

·       Problem in main steam ejector.

·       Vacuum breaker is passing.

 

4.      Specific fuel consumption:

Specific fuel consumption (Kg/KWh)= Fuel consumption in Kg / Total generation in KWh

Increase in Sp. Fuel consumption will increase the heat rate. Fuel combustion should be proper.

5.      Leakage/ passing of valves:

Effect-

·       Increase in makeup water consumption.

·       Heat loading to the condenser may also increases due to passing of valves.

Detection-

·       Thermography – by monitoring the temperature of pipes down stream of valves.

·       Measuring noise level near the valve.

 

6.      Dry flue gas loss:

Reason –

·       Slag accumulation on the furnace wall reduces the heat absorption in the furnace and resulting more heat being passed in to convection zone, steam generation in water wall decreases and increase in fuel and air flow.

·       Deposition in heat absorbing surfaces, water wall, super heater,  reheater,  economize tubes, APH, reduces boiler efficiency.

·       Improper air/fuel balance  in each burner.

 

7.      Excess oxygen:

Low excess air levels can lead to unstable combustion with the potential for furnace "puffs” and resultant damage to water wall and other areas of boiler.

Insufficient excess air results in –

·       Increased slagging of water wall and super heater section.

·       Increased corrosion rates of SH and RH tube.

·       Burner chocking and nozzle damage.

·       ESP fire.

When carbon burns to CO, one third of the potential energy of carbon is released.

 

8.      APH tube leakage:

Reason –

·       Erosion due to flue gas flow.

·       Dew point corrosion.

Effect of APH tube plugging –

·       Reduction in available heat transfer surface and increase in APH outlet gas temperature. This reduces boiler efficiency and increase fuel consumption.

·       Increase in the velocity of flue gas. This results erosion and increase in Auxiliary power consumption.

 

9.      Unburnt in ash:

Reason –

·       Burner problem.

·       Insufficient excess air.

·       The non uniform distribution of air or fuel between the burner.

·       Insufficient or improper distribution of secondary air.

 

Action to be taken –

·       O2 % at economizer outlet should be maintained close to design value.

·       Air temperature should be kept high.

·       Correct differential pressure should be maintained the windbox and furnace.

·       Secondary air should be properly distributed between the burners.

 

10. Main steam (throttle) pressure before ESV:

An increase in throttle pressure, increase both  turbine cycle efficiency and turbine output.

 

11. Main steam temperature before ESV:

Decrease in main steam temperature increase heat rate in certain proportion.

 

12. Super Heater attempreration:

There is minor heat energy loss when feed water is added Super Heater steam.

Other ways to control steam temperature –

·       Adjust air flow.

·       Readjustment in secondary air distribution control.

      

Performance monitoring parameters and their calculations:

1.      Gross generation = total electrical output from generator terminal.

2.      Net generation = Gross generation – Auxiliary Power Consumption

3.      Gross heat rate = the heat energy in kcal input required to generate 1 KWh of electricity.

                            = (Gross turbine heat rate (kcal/KWh)/ boiler efficiency %) x 100

4.      Gross turbine heat rate = (heat Input to turbine (kcal/KWh)/ Generation (KWh)

5.      Net heat rate = (Gross heat rate/ Net generation) x 100

6.      Availability factor = average of the daily average declared capacity for all the days during that period expressed as a % of the installed capacity minus normative APC in MW.

7.      Availability factor (on Bar) = (operating hours of unit over reference period/total hour in the reference period) x 100

8.      Declared Capacity = capability of the generating station to deliver ex-bus MWh, declared by the generating station.

(Full declared capacity = generation – APC)

9.      Loading Factor = it is the percentage ratio of PLF and AF on bar.

10.  Partial Loading (%) = (100 – loading factor in %)

11.  Forced Outage = an outage of the generating unit due to fault or other reason, which has not been planned.

FO % = (forced outage hours of the unit over the reference period/ total hours in the reference period) x 100

12.  Makeup water consumption % = makeup water consumption (MT)/(total MCR capacity of boiler in TPH x reference period in hours x AVF on bar)

13.  Specific oil consumption = oil consumption/ total gross generation

14.  Specific fuel consumption = fuel consumption/ total gross generation

15.  Unburnt carbon loss

16.  Stack losses = the heat in the flue gas that is lost to atmosphere upon entering the stack. Stack loss depends upon fuel composition, firing conditions and flue gas temperature. They are the total of two types of losses -

·       Dry flue gas loss = the sensible heat energy in the flue gas due to the flue gas temperature.

·       Wet flue gas loss = Flue Gas Loss Due to Moisture, the (latent) energy in the steam in the flue gas stream due to the water produced by the combustion reaction being vaporized from the high flue gas temperature.

17.  Gross calorific value

18.  Unit tripping

19.  Operating hours

 

Efficiency Gap Analysis:

1.      Slag accumulation on the furnace wall reduces the heat absorption in the furnace and resulting more heat being passed in to convection zone, steam generation in water wall decreases and increase in fuel and air flow.

2.      Deposition in heat absorbing surfaces, water wall, super heater,  reheater,  economize tubes, APH, reduces boiler efficiency.

3.      Improper air/fuel balance  in each burner.  that unit are running at rated parameters to achieve design efficiency.

4.      Identify deviations in parameters which are affecting the efficiency of the unit.

5.      Identify the reason for below reason and make action plan to reduce.

I.                   High fuel consumption

II.                 High Auxiliary power consumption.

III.              Make up water consumption.

6.      Check that efficiency monitoring system is followed fully.

7.      Check that all efficiency tests as envisaged are carried out as per standard procedure and schedule.

8.      Whether suitable provisions of parts have been made in the unit for using off line instruments.

9.      Whether test procedures are available with performance testing group.

Availability  Based Tariff Gap Analysis:

ABT Components -

1.      Capacity charges – capacity charges are payable against the PLF.

2.      Energy Charges – energy charges are applied based on the actual energy drawn by the consumer.

3.      Unscheduled Interchange Charges – it is difference between an entity's actual interchange and it's schedule for a given time back.

 

Efficiency Tests:

1.      Boiler:

·       Boiler efficiency test is carried out to find out various heat losses.

·       Efficiency test line oxygen survey in boiler to determine the air ingress in the boiler system.

·       BFP performance test.

·       Fan efficiency test.

·       Auxiliary power consumption test.

·       Air tightness test in boiler system.

 

2.      Turbine:

·       Turbine cycle heat rate test.

·       Turbine pressure survey.

·       Turbine cylinder efficiency.

 

3.      Condenser :

·       Flood test

·       Online leak detection test is carried out to achieve – terminal temperature difference, air vapor depressions and

loss in condenser back pressure due to

CW inlet temperature,

CW flow,

Condenser dirty tube,

Heat loading in condenser.

 

4.      Deaerator :

·       The deaerator performance test (as per ASME PTC 12.3 – 1997).

·       The deaerator drop test is carried out to determine the water/steam leakage in the system.