Kraft Recovery Boilers – Waterside
In order to create steam, high pressure water is pumped through tubes within the boiler. Fuel burned within the boiler supplies the heat which creates steam. This module describes boiler feedwater treatment, the importance of a boiler economizer, and the functions of the primary components on the waterside of a kraft recovery boiler.
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Learning Objectives
• Describe why water is treated before being sent to the boiler
• Describe how water is treated before being sent to the boiler
• State the importance of sending feedwater through the economizer
• Describe the primary function of the steam drum
• Describe the principle behind the circulation loops within the boiler
• Identify methods of steam drum level control
• Describe the function of the superheaters
• Describe the purpose of an attemperator
• Identify and describe the safety hazards and guidelines associated with recovery boiler waterside
• Explain the flows of condensate and makeup water to the boiler
• Describe the flow of water and steam within a recovery boiler
Specs
| Course Level | Intermediate |
| Languages | English, Portuguese, Polish, Russian |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
What is unique about feedwater pumps?
Boilers operate at high pressure. The water which goes to the boiler must exceed the boiler pressure, so feedwater pumps are high pressure pumps.
What is the role of the economizer?
The economizer is a set of heat transfer tubes in the exiting flue gas from the boiler. Heat is recovered from the flue gas and is used to heat inflowing feedwater.
What is the role of the superheater?
After steam leaves the steam drum it flows through tubes in the hottest part of the boiler and becomes superheated.
What is the steam drum?
Most of the circulation tubes in the boiler terminate at the steam drum. In the steam drum, steam is allowed to separate from boiling water.
How is water circulated through the waterwalls of a boiler?
Water circulates through the water walls due to natural convection. Hot water is less dense and rises, cooler water is more dense and flows to the lower areas of the circulation system.
Sample Video Transcript
In order to optimize the efficiency of the boiler, the relatively cool feed water is pre-heated using hot flue gasses before it flows to the steam drum of the boiler. After leaving the generating bank, the flue gas is still quite hot. This gas flows through an economizer which contains heat transfer tubes similar to the boiler tubes. As incoming water flows through these tubes, the water is heated and gas surrounding the tubes is cooled. Because some of the heat in the gas is returned to the boiler, the overall efficiency of the boiler is increased. Sometimes, there are multiple banks of economizer tubes. In this case, the flows are routed in a counter current fashion such that the coolest incoming water contacts the coolest outgoing gas.
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