Recovery BLOX System Overview and Principles
Some recovery boilers use waste heat from the combustion gases to evaporate water from incoming black liquor. This increases the efficiency in the amount of steam produced by the boiler. In direct contact evaporators, hot combustion gases directly contact black liquor. This concentrates the black liquor using waste heat, but it also adds unwanted emissions of malodorous sulfur gases to the flue gas. The black liquor oxidation (BLOX) system is designed to pre-treat the black liquor to minimize these emissions. This module covers direct contact evaporators and the theory and operation of the BLOX system.
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Learning Objectives
• Define the term TRS
• Define the term BLOX
• Explain where TRS comes from
• Identify and describe a cascade direct contact evaporator
• Identify and describe a cyclone direct contact evaporator
• Describe where direct contact evaporators fit into the kraft recovery process
• Explain the principle behind a black liquor oxidizer
• Describe where black liquor oxidizers fit into the kraft recovery process
Specs
| Course Level | Intermediate |
| Languages | English |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
What does BLOX stand for?
BLOX is an ancronyn for Black Liquor Oxidation System.
Why are BLOX systems used?
BLOX systems are used in recovery boilers which have direct contact evaporators to lower the total reduced sulfur emissions in the boiler flue gas stream.
What is the primary compound that BLOX systems are trying to eliminate?
BLOX systems are used to lower the emission of TRS compounds, primarily hydrogen sulfide (H2S), in flue gas coming from recovery boilers with direct contact evaporators.
What is a direct contact evaporator?
Direct contact evaporators increase the solids in black liquor going to a recovery boiler by first contacting it with the hot flue gas coming from the boiler.
What is the principle of operation of a BLOX system?
The BLOX system uses oxygen to oxidize TRS compounds into more stable sodium compounds which do not enter the flue gas stream in direct contact evaporators.
Sample Video Transcript
Cascade evaporators are typically positioned between the boiler economizer, and the electrostatic precipitator. A cascade evaporator is a large vat that holds the black liquor, and is connected to the boiler by large duct work. A cascade evaporator is usually located near the economizer to minimize the duct work. A cascade evaporator contains one or more large drums made of horizontally aligned tubes attached on the ends to round metal plates that create a cylindrical drum. There are spaces between the tubes that allow gases to pass through. The drum sits in the vat of black liquor and slowly rotates, picking up the black liquor on the tube surfaces. The combustion gases flow through and around the tubes, heating and evaporating water from the black liquor.
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