CN1057360C - Alkali recovery from waste liquid of grass pulp papermaking by multi-point drying and burning - Google Patents

Abstract

The present invention discloses an alkali recovery technology from steaming waste liquid of straw pulp papermaking by multi-point drying and combustion, which comprises that a residual heat evaporation drying condition is additionally set on the basis that straw pulp is dried step by step in the process of falling in an evaporator, a flue and a furnace by a preheater, namely that the exterior of the furnace is additionally provided with a flame residual heat direct heat transfer, mass transfer and exchange evaporation tower, a hot wind flow promotion device is arranged in the front of an injection pump for the black liquor, and black liquor enters the furnace, passes through a drying chamber and falls into an equilizing bed of a combustion chamber to carry out combustion by contacting flames. Liquor obtained by combusting black ash of the black liquor is sodium carbonate, sodium carbonate liquor is conveyed to a causticizing workshop and is causticized to obtain liquor alkali, and the liquor alkali is recovered for adjuvant materials for steaming papermaking.

Description

A kind of papermaking straw pulp cooking waste liquor multi-point drying and burning alkali recovery process

The present invention relates to the papermaking wastewater alkali recovery process, be meant that specifically a kind of papermaking straw pulp cooking waste liquor multi-point drying and burning alkali reclaims, the black liquor vaporizing and the burning alkali that are applicable to 2000 tons to 30,000 tons non-wood-fibers of year papermaking ability (as the Straw Pulp fiber) paper mill reclaim, and have the practical art that small investment, operating cost are low, environment protection treating is effective and the method for science.

The requirement of papermaking wastewater when evaporation concentration be the wood pulp solid content by 13-19%, evaporation and concentration is to 55-56% (percentage by weight), solid content can't directly be burnt by the black liquor of 8-11% evaporation and concentration to 45-50% in the straw pulp.If make it become moisture only be the grey black of 10-15%, also must add certain sintering agent and can produce burning, and carry out some physical reactions and form NaOH and vulcanized sodium to realize recovery.But because the straw pulp silicon content is higher, silicon content is also higher relatively in the wood pulp, and when straw pulp and wood pulp excessive concentration, viscosity also increases, and the fiber relative amount is many.Cause concentrator to play dirt easily like this, the phenomenon of line clogging, therefore the technological process meeting is interrupted, and causes production undesired.Avoided dirty situation, temperature is brought up to more than 300 ℃, and difficulty is higher.

Thereby, present alkali recovery process is because heat energy need be dried to 85-94% with the wood pulp solid content by 13-19% through multiple-effect evaporation with black liquor after transforming, straw pulp is dried to 85-90% from 8-11%, make it to become the flammable grey black that contains moisture 10-15%, reach black liquid consistency more than 40% from evaporation section, technology and equipment operation all can not be normal.Evaporation section technology and equipment guarantee that black liquor vaporizing normally moves, and black liquid consistency must reduce.When black liquor was gone into stove, concentration was low excessively, needed to come dry black liquor with fuel oil as combustion adjuvant, had not only increased the production run cost, and contaminated environment.For realizing black liquor normal service requirement of each workshop section in above-mentioned technology and equipment, the wood pulp of low concentration, straw pulp black digestion liquid must be in preheater, evaporimeter, flue and stove step by step drying make that solid content is dried to moisture content 10-15% in the black liquor, reach the purpose that sodium carbonate is reclaimed in completing combustion.Wherein, dehydration about 45% in preheater, evaporimeter concentrate drying process, solid content reaches about 60-65% in the wood pulp, solid content reaches about 50-55% in the straw pulp, although wood pulp, straw pulp are concentrated, but also make preheater, evaporator pipeline play dirt, just cleaned once in 3-5 days, particularly be mixed with thin staple fibre owing to the straw pulp silicon content is high.It is quite serious to play dirty phenomenon; For the evaporation black liquor causes difficulty.Can not guarantee that the alkali stove normally stably works, can't be in the stove internal combustion, the fuel oil that also need rely on furnace temperature and replenish continues dry concentrated black liquid in stove, make the black liquor solid content of wood pulp content 60-65%, straw pulp content 50-55% bring up to 85-90%, keep furnace temperature normal physical-chemical reaction to take place simultaneously 900-1000 ℃ of ability; Concentrated black liquid must be in spray gun sprays into stove, it is vaporific at first to rely on spray gun pressure that concentrated black liquid is formed, a material that leans on interior high temperature of stove and wind-force vaporific black liquor to be formed 4 millimeter sizes then, and under the wind-force effect, a black liquor material from top to bottom falls into alkali stove bottom equalizing bed at the stove inner suspension, dropping to the equalizing bed journey time is the most favourable drying time of black liquor, but at this section in the period, black liquid consistency does not also reach 85-90%, contact promptly and can not burn with flame, can only be combustion-supporting by aftercombustion oil, price of fuel oil costliness, operating cost height, some unit takes to improve alkali stove height at present, increase the drying time that black liquor drops to equalizing bed,, bring investment excessive too much with maintenance cost but the cost of stove is too high to reduce replenishing of fuel oil as far as possible.Generally speaking, reclaim drying process according to existing alkali, black liquor is along with technological process and equipment during the starting point burning, can not guarantee that the black liquor drying contains the grey black of moisture 10-15% when reaching burning, does not just break away from height and these requisite measures of made-up fuel oil of raising alkali stove in stove.

Purpose of the present invention just is to provide a kind of new spent lye that combines with equipment to reclaim technology, be that multi-point drying and burning reclaims this technology of technology, it is to reclaim in the equipment that drying process adopted at original alkali, sets up drying equipment and device, and black liquor is gone into the concentration of stove at 35-50%.Needn't improve the height of alkali stove or use fuel oil, this technology is reducing on half the basis of equipment investment, in the multi-point drying technological process apparatus, keep certain temperature, concentration, viscosity, vacuum, flow velocity, but can keep the alkali recovering effect constant, flow process in service is unimpeded simultaneously, and black liquor is dried to the requirement that conforms with burning.

Multi-point drying and burning alkali recovery process provided by the present invention is: adopt three grades of two net filtration machine back washings to extract more than 80% in detergent milk, the rare black liquor of Baume concentration more than 5-6, in 40-50 ℃ insulated and stirred storage tank, stir then, the black liquid consistency of this moment is 8-11%, rare black liquor is sent into preheater steam by sump pump and is heated up, preheater design triple effect, the operation triple effect, wherein an effect temperature is 60-70 ℃, two effect temperature are 95-98 ℃, evaporation drying for the first time heats up when sending into evaporimeter when black liquor heats near boiling, evaporimeter adopts quadruple effect or five to imitate, temperature rose to 120-140 ℃ when black liquor entered first effect, air pressure is controlled between the 0.5-1.5 kilogram, two imitate air pressure between the 0.5-0.8 kilogram, air pressure is zero during triple effect, quadruple effect becomes negative pressure, vacuum is the 680-720mm mercury column, coolant water temperature is below 40 ℃, wherein waste liquid remains on 2-4m/s at the heating clamber flow velocity, go out to imitate concentration and remain on 30-35%, the black liquor of 30-35% is sent into the vaporific drying of formation in the waste heat evaporating column, make black liquid consistency improve 10-20%, thereby reach the requirement that flue gas cool-down dedusting and black liquor vaporizing concentrate, at this moment the concentration of black liquor reaches between the 45-50%, and the flue gas dew point temperature must be controlled at more than 80-100 ℃, and alkali stove waste heat directly evaporates black liquor, no longer establish facilities such as boiler in the alkali stove, avoid accidents such as alkali stove blast; Black liquor is through insulation, the short stream of hot blast device, and when entering the stove inner suspension and being dried to water content 10-15%, the combustion chamber, whereabouts.

It is the basis that technological basis 4.0-6.5/13 type of the present invention sprays stove, be provided with boiler combustion mode and outside stove that wind-force suspension drying combines in waste heat black liquor vaporizing tower and the stove, guaranteed that black liquor has enough baking temperatures and drying time, the grey black water content is guaranteed at 10-15%, contact flame promptly burns, and need not use fuel oil.

Technology of the present invention need not increase the height of alkali stove, and the waste heat evaporating column is set outside stove on the contrary.Make full use of furnace temperature evaporation and concentration pavilion liquid, improved black liquor temperature, reduced black liquor viscosity, guaranteed that black liquor has the newtonian liquid flowability under higher concentration, also saved steam supply, reduced operating cost.

The present invention falls in technology preheater, evaporimeter, flue, stove on the dry step by step basis, the outer waste heat evaporation equipment device heat transfer of level stove, mass transfer exchange drying have been increased again, the short stream of hot blast of peace device before the black liquor jet pump, black liquor enters and forms the vaporific alkali stove bottom equalizing bed contact flame combustion that directly drops in the stove, liquid behind the black-liquor combustion is sodium carbonate, carries out alkali after the sodium carbonate liquid causticization and reclaims as boiling papermaking auxiliary material.

Wherein, in the evaporator dry stage, it is stable that feed liquor concentration, feed liquor amount, air pressure, vacuum, cold pin water etc. must keep, and the black liquor phenomenon is run in control during operation, has so both saved steam, prevents the plugging phenomenon again.

Black liquor moisture content constantly evaporation becomes steam, is drawn by air-introduced machine.Under the effect of higher furnace temperature, black liquid consistency 45-50%, promptly incendivity has been saved operating cost, is convenient to operation.

Wherein, black liquor is gone into stokehold concentration, viscosity is higher, and insulation does not reach certain requirement again, with the liquid pump injection apparatus, has certain difficulty by the road.This technology replaces the black liquor jet pump with bitumenpump, parameter when viscosity, temperature, concentration, pressure and the black liquor when spraying because of the pitch pasta gone into stove is basic identical, therefore, before jet pump, install the short stream of black liquor hot blast device additional, hot blast is by in the air preheater circulated air being sent into the combustion chamber, temperature is about 150 ℃, and pressure is decided with the air blast design.

Wherein, stove internal combustion temperature is at 900-1000 ℃, and the straw pulp black liquor caloic is lower, and the waste heat of hothouse is absorbed by boiler and water-cooling wall, dry unfavorable to black liquor, and like this, black liquor is gone into stove concentration requirement solid content height.Bring difficulty to black liquor vaporizing is concentrated, viscosity is excessive, and is mobile poor.The relevant devices of absorption heat such as boiler is not set in stove among the present invention, and this has been equipped with safety to the alkali stove and accessory.The hothouse waste heat is sent into the waste heat evaporating column through flue.Black liquor forms vaporific at evaporating column, alkali stove waste heat directly evaporates, black liquid consistency is brought up to 10-20%, even paper plant's slurrying amount is many, sweeping situation, also the boiler that steams can be located at outside the stove, superfluous heat be converted into use after steam send steam turbine or desuperheat, evaporimeter washes once with 200 kilograms of jetting machines at two weeks or one month (paper plant that has is in a season), to remove slight tube wall incrustation scale, be beneficial to better conduct heat evaporation effect.

Fig. 1 is a process chart of the present invention

Technology of the present invention can use the height of fuel oil or raising alkali stove just can reach Arrive good recovering effect, and can save the investment of half.

Claims (1)

1. a papermaking straw pulp cooking waste liquor multi-point drying and burning alkali recovery process is included in to wash in the slip and extracts more than 80%, and the rare black liquor of Baume concentration more than 5-6 stirs in 40-50 ℃ insulated and stirred groove then; The black liquid consistency of this moment is 8-11%, and rare black liquor is sent into preheater by sump pump and begun the steam intensification; Preheater design triple effect, operation two is imitated, wherein an effect temperature is 60-70 ℃, two imitate 95-98 ℃ of temperature, finish the intensification evaporation drying of boosting when two black liquor of imitating are sent into evaporimeter near boiling the time, evaporimeter adopts quadruple effect or five to imitate, temperature rose to 120-140 ℃ when black liquor entered first effect, air pressure is controlled between the 0.5-1.5KG, two imitate air pressure between 0.3-0.8KG, air pressure is zero during triple effect, quadruple effect becomes negative pressure, vacuum is the 680-720mm mercury column, coolant water temperature is below 40 ℃, wherein waste liquid keeps 2-4m/s at the flow velocity of heating clamber, go out to imitate concentration and remain on 30-35%, the concentrated black liquid of 30-35% is sent in the evaporating column formed vaporificly, and rely on alkali stove waste heat and flue gas mass transfer, conduct heat and exchange evaporation drying, reach black liquor 45-50% concentration, temperature keeps more than 80-100 ℃ in the tower, and black liquor is through insulation, and hot blast is urged the stream device, enter stove inner drying chamber combustion chamber, the dry whereabouts contact equalizing bed flame combustion that suspends, waste heat directly evaporates black liquor, when black liquor is dried to water content 10-15%, forms completing combustion, white black liquor after the burning promptly is the higher sodium carbonate liquor of content, sends into the alkali caustic room thereafter.

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