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September 14, 2020

BEST PRACTICE NO. 66 – STEAM SYSTEM THERMAL CYCLE EFFICIENCY

What Is the steam system thermal cycle efficiency?

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In this Inveno Engineering, LLC Best Practice will be discussed what is “Steam Thermal Cycle Efficiency” are what affects the efficiency.  In the next Best Practice will be the corrective measures that need to be implemented to increase the efficiency.

A question that all steam system managers need to answer is the steam system thermal cycle efficiency.  The average steam system thermal cycle efficiency is 58%, which means that 42% of the energy that is consumed in the boilers is wasted or loss.  To utilize all the energy input into the boilers is not achievable and the operation will have a few acceptable losses, but a high percentage of losses can be prevented or eliminated.

Total fuel energy or Btu’s input into the boiler to generate the steam

Minus

Btu’s that are recovered and delivered back to the boiler plant

  • When benchmarking the thermal cycle, the sensible energy in the condensate and quantity that is delivered back to the boiler is considered the recovered energy.
  • The deaerator uses steam from the main steam line maintain pressure and temperature on the deaerator, therefore can not be the benchmark for recovered condensate.steam system items that can affec the steam system thermal cycle efficiency

All items that can affect the steam system thermal cycle efficiency need to reviewed and no item can be over looked.  Each item can contribute significant losses if not properly managed.

1.1.  Steam generation

·       Boilers

·       Steam Turbines

1.2.  Steam distribution

·       Piping

·       Steam leaks

·       Insualtion

·       Valves

·       Expansion devices

·        Steam traps stations

1.3.  End users

  • Shell and tube heat exchangers
  • Plate and frame

1.4.   Condensate systems

·       Condensate lines

·       Flash steam losses

·       Pumps

·       Condensate leaks

·       Condensate losses

·steam Generation Losses?

The first area that needs to reviewed in the steam generation, which can contribute a significant energy loss even before the steam is distribute into the steam system.

1.5.    Boiler Flue Gas

The boiler has on the average 16.4% energy loss due to the flue gas volume and the elevate temperature of the gases from the combustion process.  The boiler can have several devices to lower the flue gas losses which will be discussed later on in this technical paper.

1.6.    Boiler Outer Shell or Casing Losses

The outer shell or casing of the boiler will contribute a low loss percentage (.5%), which is a acceptable loss as long as the boiler casing does not have hot spots or above normal temperatures.  The plant should have an infra-red camera scan of the casing at least once a year in not more.  The data is benchmark to detect fatigue of the boiler internal insulation.

1.7.    Boiler Continuos Blowdown

There are two blowdown systems on a boiler; one of the blow downs is the continuous blowdown that is continually skimming just below the boiler water level.  The estimated energy loss from the continuous blowdown is .1.5% which will greatly depended on a number of factors that are discussed in other SEA Best Practices.

 

1.8.    Boiler Bottom Blowdown

The other blowdown that occurs on the boiler is the bottom blow from the lowest water containment area of the boiler.  The estimated energy loss from the bottom blowdown is .2% which will greatly depended on a number of factors that are discussed in other SEA Best Practices.

1.9.    Steam Turbine

The loss of mechanical work from reducing steam pressures with a control valve and not using a steam turbine for the pressure reduction is not added into our thermal cycle losses.  A rule of thumb to use is 75 lbs of steam per hour is equal to 1 horsepower of work from a steam turbine.

boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

1.10.                   Steam Leakage

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

1.11.                   Heat Transfer Insulation

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

 

1.12.                   Steam Trap Station Failures

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

 

1.13.                   Condensate Line and Component Insulation

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

1.14.                   Steam Venting to Atmosphere

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

The following engineering review goals were set forth in communication prior to the SEA engineers arriving, during the pre-engineering meeting, and in daily plant meetings that occurred during the on-site visit by SEA engineers.STEAM DISTRIBUTION

High Steam Pressure in High-Pressure Boiler Drum

The high steam pressure over pressurization occurrences in the high-pressure drum at or near the maximum output of the gas turbine has forced the plant to reduce the MW output of both the gas turbine and the steam turbine. The reduction of MW output has had a dramatic effect on the plant operation and caused a financial loss.

The accumulation of pressure results in over pressurizing the high-pressure drum and causes the high-pressure drum safety valves to lift and relieve the excessive pressure. This typically occurs 30 to 60 minutes after the gas turbine and HRSG units obtain full capacity. The safety valve lifting will cause the safety valves to operate unreliably and will cause energy loss from the loss of steam to atmosphere. The other method of relieving steam pressure is from the automatic vent valve system, but the venting of steam results in energy losses.

The accumulation of excessive pressure in the boiler drum has recently occurred and was not an issue at the startup of the plant operation. There have been upgrades to the gas turbine; SEA will review these upgrades to determine whether they are a factor in the over pressurization.

Re-rating of the High Pressure and Intermediate Pressure Drum on the HRSG

One solution to correct the excessive pressure that was discussed was the re-rating of the HP and IP drum on the HRSG. The pressure re-rating would take recalculations and approval from all agencies involved. This action would be a last resort effort, and the end result might not be successful.

 

1.15.                 General Review of the Steam System

SEA conducted a general overview of the steam system that included but was not limited to the steam piping, steam flow metering, steam turbine, condenser, high temperature water system, deaerator operation, and the condensate return system.

END USERS

The original performance testing benchmarks for the system were documented from the Harris Group (documented on March 21, 2005) for the upgrade to LM 6000. See Addendum 6.CONDENSATE SYSTEMS

The performance testing for the gas turbine, HRSG, and the steam turbine was conducted on April 14, 2011.

 

1.16.                 Test Points

The SEA team carefully selected test points that would help trend and evaluate the current operation of the gas turbine, HRSG, and the steam turbine. All points were field located, and the points captured are listed below in Table 1 for reference.

 

1.     CORRECTION METHODS

To accurately benchmark the cogeneration facility, a comprehensive selection of the necessary data points was identify

 

1.17.                 Test Points

The SEA team carefully

 

The boiler has on the average 16.4% energy loss due to the flue gas volume and the elevate temperature of the gases from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer
    • Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110o The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flue gases are lowered to the 110oF temperature of lower.
  • Standard air heater
    • The air heater is an heat exchanger that reduces the flue gas losses by heating the incoming air to the combustion process.
  • Condensing air heater
    • Decreases the flue gases temperature by heating the incoming air for the combustion process or heating another air requirement and reducing the flue gas temperature at or below 110o  The condensing air heater unit  will bring the boiler efficiency to 93% depending on the several factors.

1.18.                   Boiler Blowdown

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

 

 

1.19.                   Steam Line Insulation

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

1.20.                   Steam Leakage

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

 

1.21.                   Heat Transfer Insulation

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

1.22.                   Steam Trap Station Failures

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

 

1.23.                   Condensate Line and Component Insulation

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu

1.24.                   Steam Venting to Atmosphere

The boiler has on the average 16% energy loss due to the flue gas volume and elevate temperature from the combustion process.  The boiler can have several devices to lower the flue gas losses which are as follows:

  • Standard economizer
    • Decrease the flue gases losses by heating the feedwater to the boiler. Typically, this will increase the boiler efficiency to 86%.
  • Condensing economizer

Decreases the flue gases temperature by heating a liquid medium or heat sink and lowering the flue gases outlet temperature from the combustion process below 110oF.  The condensing economizer will bring the boiler efficiency to 93% depending on the several factors.  The disadvantage with the condensing technology it can only be applied to plants that have large volume of liquid that requires heating to insure the flu