STEAM LEAKS

 

Use ultra sonic and thermal detection technology to identify steam leaks. Label the leaks, record them on a list, prioritize the leaks and fix them accordingly.

 

  

 

 

GENERAL TIPS

• Insulate all exposed steam, hot water pipes,  valves, condensate return lines and repair damaged insulation

• Record down the locations of the all the steams traps and inspect steam traps for leaks on a regular basis. If steam can be seen billowing out of the trap it means that it has failed, ensure it is fixed asap
• Monitor the conductivity of the condensate to ensure the boiler is operating efficiently
• Ensure the heat transfer surfaces within the boiler is regularly maintained and kept as clean as possible.
• Install heat recovery equipment (i.e. feedwater economizers and/or combustion air preheaters using flue gas)
• Improve water treatment facilities to reduce boiler blow down

 

BOILER

 

Combustion Efficiency

 

Operating the boiler with the optimal amount of air will minimize the heat loss up the stack and improve combustion efficiency. Combustion efficiency is a measure of how effectively the heat content of a fuel is transferred into usable heat. The stack temperature and the flue gas O₂ (or CO₂) concentrations are primary indicators of combustion efficiency.

 

Assuming complete mixing, a stoichiometric amount of air is required to completely react with a given quantity of fuel. In practice, combustion conditions are never ideal, and additional or “excess” air must be supplied to completely burn the fuel.

 

The correct amount of excess air is determined from analyzing flue gas O₂ or CO₂ concentrations. Inadequate excess air results in unburned combustibles (fuel, soot, smoke and CO); while too many results in heat lost due to the increased flue gas flow – thus lowering the overall boiler fuel-to-steam efficiency.  Ways to ensure the combustion process is efficient is to:

 

• Refer to the burner’s original design conditions and identify the optimum air to fuel ratio and then monitor the flue gas O₂ or CO₂ on a regular basis accordingly, to ensure it meets the requirements
• Refer to the “Energy Efficient Burner” section for further information

 

 

Boiler Water Heat Transfer Tubes

 

Scale or fouling are formed by the build up lf calcium, magnesium and silica, and can reduce the efficiency of the boiler. Up to 2% more energy is required for water tube boilers and up to 5% for fire tube boilers with scaled tubes.  Check the following to ensure the scaling in the boiler is under control:

 

1. Monitor the flue gas temperature, an increase of flue gas temperature may indicate that there is a build up of fouling or scaling.
2. During plant shut downs, visually inspect the tubes for scaling, implement a regular check up in the maintenance schedule

 

If the scaling is a lot more often than intended by the boiler’s manufacturer, speak to the water treatment contractors for advice. Ensure the feed water treatment plant is effective.

 

Condensate Return

 

Returning hot condensate to the boiler will increase the boiler’s efficiency. Increase in condensate return will result in decrease in make-up water, fuel consumption, chemicals use and treatment costs. Ways to improve condensate return:

 

1. Repair steam distribution and return line leaks
2. Insulate condensate return piping
3. Repair malfunctioned steam traps

 

Boiler Blow Down

 

When water evaporates it leaves behind a build up of solids present in the feedwater. This forms a sludge or sediment in the boiler. Some form suspended solids or total dissolved solids (TDS) and to ensure the boiler is operating at its best, the boiler is blown down on a regular basis to remove these impurities. Insufficient blow down may cause formation of deposits and carryover of water into the steam system. Excessive blown may increase in unnecessary energy, water, and chemicals use. Optimizing the boiler blow down ensures the amount of make up water consumed is maximized and therefore the optimizing the amount of energy, chemicals and treatment required. Ways to optimize blow down include:

 

• Investigate into a automated blow down system that regulates the amount of blow down in relation to the amount of TDS in the water
• Look into installing a blow down energy recovery system using a heat exchanger, flash tank etc. This will decrease the temperature of the waste water discharged off site and also the amount of cooler fresh water use
• Check to ensure the water treatment system is operating properly if all the other areas have been addressed

 

High Pressure Condensate Recovery

 

Typically, low pressure steam requirements are met through the throttling, of high pressure steam. This may not be the most efficient use of high pressure steam. In some circumstance the low pressure steam can be obtained through the flashed high pressure condensate. Flashing is particularly feasible when it is not appropriate to return the high pressure condensate to the boiler.

 

The table below provides the corresponding amount of low pressure steam in relation to the amount of high pressure condensate pressure.

 

	Low Pressure Steam
High Pressure Condensate (psig)	@ 50 psi (lb/lb)	@ 30 psi (lb/lb)	@ 15 psi (lb/lb)	@ 5 psi (lb/lb)
200	10.4	12.8	15.2	17.3
150	7.8	10.3	12.7	14.9
100	4.6	7.1	9.6	11.8
75	2.5	5.1	7.6	9.9

 

Hint: Look for continuous high pressure condensate sources.

 

Powering Absorption Chillers with Low Grade Steam

 

Low grade steam can be used to power absorption chillers. Low pressure, steam driven absorption chillers are available in capacities of 100 to 1,500 tons. This is especially effective when the low grade steam is not reused and discharged and chilled water is required on the plant.

 

Contact your local chiller supplier for more information on how this can be done.

 

Deaerators

 

Dissolved gases exist in fresh feedwater and they need to be removed to protect the system from corrosion. The purpose of the deaerator is to protect the boiler and steam system from corrosion by removing dissolved gases. Deaerators use steam to heat the water to its full saturation temperature corresponding to the steam pressure in the deaerator and bubbling of the water separates the dissolved gases and discharges it. Ways to optimize the deaerator include:

 

• As the deaerator uses steam, ensure it is adequately insulated to minimize heat loss
• The deaerator is designed to remove dissolved oxygen from the feed water and not free air from loose piping suction side of pumps due to improper pump packing. Check pumps for loose piping
• Ensure there is a designated steam pressure regulating valve to prevent a sudden surge of steam pressure, as this re-oxygenates the feedwater

 

Vessels

 

Where possible, vessels that contain heated liquids that do not need to be cooled should be covered and insulated, to avoid heat loss to the atmosphere.  The table below shows the heat loss rate (BTU/hr.ft²) in open tanks/vessels. 

 

 

 

Example:

 

The heat loss from the vessel below, assuming that the ambient temp is 65^oF the liquid temperature is at 150oF, can be calculated using the following method:

 

 

 

Assume it costs $11 per MMBTU, this means that it would cost approx $101,000 a year to heat loss.

 

Energy Efficient Burners

 

The burner is located inside of the boiler and its purpose is to mix the air and the fuel to maximize the combustion process and minimize the emissions. An efficient natural gas burner requires 2-3% excess oxygen (or 10 – 15% excess air) in the flue gas, to burn fuel without forming an excessive amount of CO. The recommended ways to ensure the burner is efficient include:

 

·         Ensure the burner does not have complex linkage systems designs that may not hold their air-to-fuel ratios settings over time

·         An alternative to complex linkage system designs are modern burners that use servomotors with parallel positioning to independently control the quantities of fuel and air delivered to the burner head. There are more controls with these types of burners

·         Conduct burner maintenance on a regular basis, this will maintain it’s efficiency longer

 

 

SOURCE:

 

1.      http://www1.eere.energy.gov/industry/bestpractices/pdfs/steamsourcebook.pdf

2.      http://www.spiraxsarco.com/resources/steam-engineering-tutorials.asp