Hello friends, welcome back to my channel Biotutorials. In this video, we will discuss about Black Liquor Recovery Boilers. Black Liquor is a mixture of organic matter and inorganic chemicals that result from the pulping process. The Black Liquor Recovery Boiler is designed to burn the volatile organic material in black liquor. for its heating value and to allow the inorganic chemicals to collect on the floor of the boiler in a molten bed referred to as smelt.
The inorganic chemicals present in smelt can be reclaimed and used to regenerate white cooking liquor essential to the pulping process. The most important criteria when selecting refractory for the black liquor recovery boiler is their resistance to the process smelt. The molten smelt that collects at the bottom of the boiler is extremely high in soda.
These sodium compounds can attack alumina-silica systems in refractory to cause low melting and all expensive phases. What does the recovery boiler do? Burn black liquor, recover inorganic chemicals, generate superheated steam.
Burning black liquors take place in the furnace section. Require black liquor and air to be intermixed. Black Liquor sprays, force air system.
Self-sustained combustion is normal. Use auxiliary fuel for start-up, shut-down, and to assist marginal combustion. Combustion gas flow driven by induced draft fan. Furnace section. Basically a rectangular box with opening for liquid, air, etc.
Lower furnace. Liquid sprayed in. combustion air enters, charbed smelt formation and drainage, upper furnace, resistance time to complete combustion, heat absorption to cool gases, air flue gas equipment, a four-start fan to deliver the combustion air to the boiler typically at three different levels an id fan to withdraw the flue gas from the boiler operate on a balanced raft recover the inorganic chemicals as a molten smelt of na2s and na2 co3 na2s required a local reduction oxygen deficient environment some s level as na2so4 Incomplete reduction, major bi-reduction efficiency, runs out of the furnace through spouts into the dissolving tank to form green liquid. Chemical recycle to furnace. Dust Na2SO4 and Na2CO3 collected in electrostatic precipitator and returned to the black liquid being fired.
In bi-roganic. that collects on heat transfer surface is removed with soot blowers and either falls directly to the heart or is collected in ash hoppers and returned to the black liquid being fired feed water heating in economizer natural circulation steam generation water valve floor roof screen effused generating rise steam temperature in superheater water and steam circuit feed water enters the boiler through economizer lower headers water vapor separation occurs in steam drum of the generating bank generating bank is natural circulation loop water flows down back side steam water flow up front circulation in two drum boiler two drum is a steam water separator hot feed water enter steam leaves Generating bank is its own natural circulation loop. Rear tubes act as downcomers.
Forward tubes act as risers. Mud drum is source of water to all other loops. Floor and water well headers. Furnace screen headers. Water and steam circuit.
Hot water then flows the downcomer to lower furnace headers and is distributed evenly to water valve tubes. Rides in water valve tubes as it is heated and enters the steam drum. A separate loop feeds the screen tubes. The separated vapor saturated steam is further heated in the superheater to produce superheated steam.
Superheated steam exits the boiler through the final superheater outlet. Circulation in one drum boiler. Everything goes to and comes from the drum.
External downcomers take water to floor and lower wall headers. External downcomers feed bottom generating bank heaters. Cross over tubes. take water from economizer outlet header to drum supply tube take steam to super heater inlet headers one drum is two drum all recoveries used to be two drums first one drum in 1984 at leaf rivers increasing size and pressure favor one drum design except of very small units All new modern recovery boilers are single drum design, super heater.
Usually serval banks with various arrangement of steam flow with gas flow may have interstage at impression. Tube back spacing in back may be tangent or spaced. This support arrangement act to do for headers generating bank. Hot gas leaves pass through a generating tank screen above the arch.
Rear water tube bent out of plane to form opening for gas to flow through. Single drum boiler. Gas flow parallel to boiler bank tubes.
Two drum boiler. Gas flow across tubes. Economizer, cross flow and parallel flow diagram shown here super heaters and economizers both have a significant increase in the fluid steam or water temperature as its flow within the tubes both are subjected to thermally induced stress difference in flow or heat pickup in parallel tubes cause different amount of expansion preferring equipment fans, liquor system, auxiliary fuel system, spouts and dissolving tank, soot blowers, precipitator, direct contact evaporator, liquor system, liquor guns, pumps and piping, mixed tank, full dust addition, liquor heaters. Solids, monitoring and automatic diverging systems Auxiliary fuel systems contain Burners and igniters Fuel piping and controls Oil and ore gas Flame safety system Monitors and interlocks Burners locations Hearth burners Used for startup and shutdown Assist in unstable firing conditions Load burners Usually above liquid guns Used for extra steam generation Spouts and dissolving tank Spouts water cooled through mounted in or furnace at spout opening near earth Spout cooling water system Agitated tank to dissolve smelt and make green liquid.
Shatter jets or other means to break up smelt stream as it enters the Tank Soot blowers Use a steam jet to remove deposits Superheaters Generating bank Economizer Large number mounted external to boiler When activated they go in and then retract Electrostatic precipitators Remove dust from the flue gas Recovered dust is recycled to black liquid precipitator efficiency determine dust load and opacity out the step direct contact evaporator final black liquid concentration step on many older recovery boilers hot flue gas brought into direct contact with black liquid ride solids from 50% to 65% solid Cools flue gas need a smelt reprimizer. Two types in use. First one is cascade evaporator. Second is cyclone evaporator.
Cascade evaporator and cyclone evaporator are shown here. So friends if you like this video then like and share. Also don't forget to subscribe this channel and press bell icon for getting notification of my upcoming videos. videos