11-10-2012, 01:33 PM
Boiler Blowdown
[attachment=36051]
Introduction
To defray energy costs, many industrial plants have their own boilers to generate steam to produce a portion of their energy needs. In addition to generating power, the steam may also be used directly in plant processes or indirectly via heat exchangers or steam jacketed vessels.
Problems
The raw water used to feed the boilers, contains varying levels of impurities that must be removed to protect the boiler and associated equipment. Pretreatment processes such as reverse osmosis, ion exchange, filtration, softening and demineralization may be used to reduce the level of impurities, but even the best pretreatment processes will not remove them all and will continuously carry some dissolved mineral impurities into the boiler.
These dissolved impurities accumulate in the boiler water when steam is made; only pure water leaves the boiler. The increasing concentration of dissolved solids leads to carryover of boiler water into the steam, damaging piping, steam traps and other process equipment. The concentration of dissolved solids increases until the boiler water can no longer hold all of them in solution and a saturation point is reached. They then begin to drop out (suspended solids) forming a sludge or scale on the boiler walls and piping.
Benefits/Solutions
The benefits for proper boiler blowdown control include the following:
• Reduced operating costs (less feedwater consumption; chemical treatment and higher heating efficiency)
• Reduced maintenance and repair costs (minimized carryover and deposits)
• Cleaner and more efficient steam
• Minimized energy loss from boiler blowdown can save about 2% of a facility’s total energy use with an average simple payback of less than one year.
The most common methodologies used for boiler blowdown control include: (1) continuous, (2) manual and (3) automatic.
Continuous blowdown utilizes a calibrated valve and a blowdown tap near the boiler water surface. As the name implies, it continuously takes water from the top of the boiler at a predetermined rate to reduce the level of dissolved solids. The rate is usually set slightly greater than necessary to be on the safe side.
Manual blowdown is accomplished at most plants by taking boiler water samples once a shift and adjusting the blowdown accordingly. This grab sample approach means that operators cannot immediately respond to changes in feedwater conditions or variations in steam demand and scaling conditions can occur and go undetected until the next sample check.
Summary
The frequency and duration required for boiler blowdown is significantly affected by the water quality. Improving feedwater quality through make-up water, chemical treatment and proper blowdown control can significantly reduce treatment and operational costs including:
I. Reduced operating costs
II. Reduced maintenance and repair costs
III. Cleaner and more efficient steam
IV. Energy Savings
Increased efficiency and reduced operating costs can be achieved by using the Yokogawa Conductivity Series line of products. Control configurations will carry with the application and the customer’s requirements.
[attachment=36051]
Introduction
To defray energy costs, many industrial plants have their own boilers to generate steam to produce a portion of their energy needs. In addition to generating power, the steam may also be used directly in plant processes or indirectly via heat exchangers or steam jacketed vessels.
Problems
The raw water used to feed the boilers, contains varying levels of impurities that must be removed to protect the boiler and associated equipment. Pretreatment processes such as reverse osmosis, ion exchange, filtration, softening and demineralization may be used to reduce the level of impurities, but even the best pretreatment processes will not remove them all and will continuously carry some dissolved mineral impurities into the boiler.
These dissolved impurities accumulate in the boiler water when steam is made; only pure water leaves the boiler. The increasing concentration of dissolved solids leads to carryover of boiler water into the steam, damaging piping, steam traps and other process equipment. The concentration of dissolved solids increases until the boiler water can no longer hold all of them in solution and a saturation point is reached. They then begin to drop out (suspended solids) forming a sludge or scale on the boiler walls and piping.
Benefits/Solutions
The benefits for proper boiler blowdown control include the following:
• Reduced operating costs (less feedwater consumption; chemical treatment and higher heating efficiency)
• Reduced maintenance and repair costs (minimized carryover and deposits)
• Cleaner and more efficient steam
• Minimized energy loss from boiler blowdown can save about 2% of a facility’s total energy use with an average simple payback of less than one year.
The most common methodologies used for boiler blowdown control include: (1) continuous, (2) manual and (3) automatic.
Continuous blowdown utilizes a calibrated valve and a blowdown tap near the boiler water surface. As the name implies, it continuously takes water from the top of the boiler at a predetermined rate to reduce the level of dissolved solids. The rate is usually set slightly greater than necessary to be on the safe side.
Manual blowdown is accomplished at most plants by taking boiler water samples once a shift and adjusting the blowdown accordingly. This grab sample approach means that operators cannot immediately respond to changes in feedwater conditions or variations in steam demand and scaling conditions can occur and go undetected until the next sample check.
Summary
The frequency and duration required for boiler blowdown is significantly affected by the water quality. Improving feedwater quality through make-up water, chemical treatment and proper blowdown control can significantly reduce treatment and operational costs including:
I. Reduced operating costs
II. Reduced maintenance and repair costs
III. Cleaner and more efficient steam
IV. Energy Savings
Increased efficiency and reduced operating costs can be achieved by using the Yokogawa Conductivity Series line of products. Control configurations will carry with the application and the customer’s requirements.