CN1247915A - Acidifying sulfate pulp-making process - Google Patents

Abstract

The present invention relates to paper making technology. The pulp making process consists of five sections of digestion, washing, acidifying, caustification and calcination. It is different from conventional sulfate process in that the black liquor is acidified rather than burnt and that the lignin burning step and the lime calcination step are combined into one integral. Acidified black liquor is deposited to separate fast in new technological method, and this makes it possible to reduce greatly the cost in alkali recovering equipment and equipment operation. The said method is suitable for pulping various fiber material, including pulping rice and wheat straw with high SiO2 content.

Description

Acidifying sulfate pulp-making process

The invention belongs to the pulping technology for paper-making field, relate to a kind of acidifying sulfate pulp-making method.

In the pulping technology for paper-making field, handle around black liquor of pulp making, multiple technical scheme was proposed, the scholar who has even pulping process also proposed the essence transformation is as anthraquinone, hyperbaric oxygenation.But, comprehensive each side factor, generally acknowledge at present effective and feasible, still (black-liquor combustion type) kraft process, widely large-scale wood pulp factory adopts.Yet there are two big disadvantages in this method: the one, complex process, the alkali recovery equipment investment greatly, and is not easy to operate, the operating cost height, concerning medium and small paper mill economically, technical all unable bearing; The 2nd, be not suitable for SiO ₂The straw pulp of rice and wheat that content is high, and China's timber resources is poor relatively general, most of medium and small paper mill are to be pulping raw material with the rice wheat straw, account for the whole nation more than 40% of output of total slurry.Therefore, run into great difficulty with being transplanted to middle-size and small-size paper mill after (black-liquor combustion type) kraft process directly transplanting or the improvement.Chinese patent: 96118204.0,96118399.3 middlely introduced two kinds of methods of handling system with black liquor, last patent application provides the method for black liquor acidification, but expense of raw materials is too high, back one method has solved the too high problem of expense of raw materials on last method basis, but secondary pollution occurred.

The purpose of this invention is to provide a kind of low pollution, economy, easy to operate and be particularly suitable for the acidifying sulfate pulp-making method of existing middle-size and small-size paper mill technological transformation.

The objective of the invention is to realize with the following methods.The present invention is at Chinese patent: 96 118204.0, the perfect a kind of pulping process of development is gone up on 96 118399.3 bases, comprise boiling, washing, acidifying, causticization and five workshop sections of calcining, wherein boiling, washing room and traditional kraft process or soda pulping process method are identical; Acidifying workshop section then is the SO that utilizes in the stack gases ₂Make the acidulant of black liquor, and the black liquor after the acidifying is carried out physical chemistry handle, allow it finish a reaction that is called black liquor acidifying pyrolysis sedimentation; Caustic room is with the Na in CaO digestion back and the acid clear liquid ₂SO ₃Produce causticizing reaction and generate NaOH and CaSO ₃Precipitation, isolated alkaline clear liquid, after dosing as the cooking liquor of cooking section; It is fuel that calcining workshop section adopts heavy oil, and using the lignin of separating from black liquor is auxiliary fuel, with CaSO ₃Be sintered into CaO and SO ₂, the SO that the calcining back generates ₂Flow back to acidifying workshop section as acidulant, the CaO that the calcining back generates sends caustic room back to and participates in causticizing reaction.

Be further described below in conjunction with process chart.

Among the figure, cooking section is by getting the raw materials ready, dosing, boiling, master operation such as spurting and form; Washing room is made up of squeezing and washing procedure; Acidifying workshop section is made up of master operations such as mixing, acidifying, preheating, precipitation, separation and dedustings; Caustic room is by lixiviate, filtration, causticization, digestion and master operation such as separate and form; Calcining workshop section is made up of master operations such as mixing, calcining and heat exchanges.Boiler provides boiling and the required heat of precipitation operation.

In the present invention, cooking section is identical with the cooking section of traditional kraft process or soda pulping process method.Washing room adopts the multistage counter current washing methods, and is identical with the washing room of traditional kraft process.Hereinafter main flow process with regard to acidifying, causticization, three workshop sections of calcining is described.

Acidifying workshop section: black liquor and washings from washing room mix in mixing pit, naturally be cooled to below 45 ℃, pump in the acidifier absorb eliminate ashes be rich in sulphur waste gas, black liquor temperature slightly rises, after the acidifying in the black liquor lignin and water form gelatinous precipitate, carry out exchange heat with high-temp waste gas again from heating boiler, temperature rises to 70～80 ℃, enter the precipitation operation and further be warming up to 90～98 ℃ with the heating boiler Steam Heating, be incubated about 30 minutes, at this moment the lignin of gelatinous precipitate constantly dewaters and all forms earth shape precipitation at last, and follows a large amount of CO ₂Emit, also taken away part steam, can become acid clear liquid and lignin precipitation with 200 order filter cloth natural separation black liquor at last.SO ₂Mainly take from the stack gases of calcining workshop section as the acidulant of black liquor, the stack gases of heating boiler only as a supplement.The high-temp waste gas of boiler is after heat exchange, and EGT is reduced to 100～120 ℃ from about 250 ℃.This two-way stack gases with the black liquor acidifying before, to carry out dedusting earlier and continue cooling and handle, so that improve the sedimentation quality of lignin.With the condensed water washing and the cooling exhaust of an amount of band acidity, waste water after water yield control is back to the dedusting operation so that improve the acidity of water for dust removal, reduces SO in the waste gas through separation circuit elimination boiler ash sediment ₂Loss.Acid clear liquid send caustic room, and the lignin precipitation is sent calcining workshop section.

Caustic room: (Main Ingredients and Appearance is Na to the slag after the burning of calcining workshop section by acid clear liquid after the acidifying workshop section precipitate and separate and lignin ₂CO ₃) enter the lixiviate of lixiviate pond after, sodium salt dissolves in the water, and heat and CO are arranged ₂Emit.Leach insoluble matter, clear liquid enters the causticization operation.Contain a large amount of Na to be recycled in the clear liquid ₂SO ₃With the small amount of alkali soluble organism.Insoluble matter mainly is CaSiO ₃The carbon black of cinder not, this is the main exit that Si discharges the circulatory system.Fully digest with condensed water earlier from the CaO of calcining kiln, also enter the causticization operation behind the thick chad of elimination.Causticizing reaction takes place in clear liquid and digestion lime in the causticization pond, generate CaSO ₃Precipitation and NaOH alkalescence clear liquid, after the isolated by filtration, alkaline clear liquid send cooking section, CaSO ₃Precipitation is sent calcining workshop section.

Calcining workshop section: in the lignin that acidifying workshop section separates, add an amount of Na ₂SO ₄, after mixing, enter calcining kiln, behind the evaporation section moisture content, enter the burner hearth burning, simultaneously the CaSO that separates at caustic room ₃After an amount of lime stone of middle adding mixes, enter calcining kiln, behind the evaporation section moisture content, enter the calcining compartment calcining.Burner hearth is interior to be main fuel with heavy oil, and lignin is only as auxiliary fuel, and the lignin ignition temperature should be higher than 1100 ℃, guarantees Na ₂SO ₄Decompose and generation Na ₂CO ₃Slag.Na ₂CO ₃Slag send the lixiviate operation of caustic room.The heat that heavy oil and lignin burning produce is by deflector guiding high temperature gas flow and CaSO ₃The particle convection current, heating CaSO ₃Particle to 820～850 ℃ make CaSO ₃And CaCO ₃Resolve into CaO, SO ₂And CO ₂CaO send the digestion operation of caustic room.The SO of high temperature ₂, CO ₂Main body with a large amount of water vapours formation kiln waste gas is used for heating lignin and CaSO earlier ₃, carry out heat exchange by heat exchanger and cold water then.Send to laundry after cold water is heated to 85～95 ℃ and wash workshop section as pulp washing water.Waste gas cools to 100～120 ℃ of dedusting operations of sending acidifying workshop section, further cools to about 70～80 ℃ in the way.Follow the cooling of kiln waste gas, have a large amount of water vapour condensations to get off, the band faintly acid is collected and is used as lime slaking and water for dust removal in the condensation pond.

There is a small amount of acid boiler ash sediment in acidifying workshop section, and caustic room has the thick slag of digestion of the thick slag of a small amount of alkaline lixiviate, and the three unifies piece, is tending towards neutral, can efflux, and also can be used for producing construction material.

The present invention is by the technical process thought of using and developing traditional sulfate process, substitute the furnace room of black liquor with the acidifying workshop section of black liquor, the black liquor acidifying then is to have utilized one " black liquor acidifying pyrolysis sedimentation reaction ", accelerated the separating rate of lignin and clear liquid greatly, make the investment and the operating cost that reduce black liquor processing and alkali recovery equipment significantly become possibility, thereby realized the acidifying remodeling of traditional sulfate process.The present invention has following advantage:

1. have the same high alkali recovery in theory, and the equipment one-time investment is its about 1/15th with traditional kraft process;

2. not only eliminated the pollution of black liquor fully, and can also eliminate the SO in the stack gases water quality ₂To the pollution of atmosphere, this also is that traditional kraft process is incomparable;

3. can realize alkali, water, lime and SO substantially in the technological process ₂Closed circulation, not only do not increase operating cost after the equipment operation, 200～400 yuan of/ton slurries on the contrary can reduce production costs on existing price level;

4. this sharp method pulping fibre adaptability to raw material is wide, comprises SiO ₂The straw pulp of rice and wheat that content is high;

5. production technology is simple, and easy operating is particularly suitable for the technological transformation that middle-size and small-size soda pulping process factory's black liquor processing and alkali reclaim;

6. can replace traditional kraft process and become the upper reaches method of paper industry, oracle will have the world, domestic vast market potentiality.

Description of drawings:

Fig. 1 acidifying sulfate pulp-making process process chart.

Embodiment: adopt pulping equipment commonly used and general acidifying, causticization and calciner, to produce the air-dry thick slurry of ton (the 900kg over dry is slightly starched) is example, and the amount of the amount of each workshop section's material input and output and the input and output of whole process cycles material is listed by table 1.Cooking section, input timber 3539kg wherein contains moisture 1643kg.Washing room, black liquor output item comprise black liquor and waste water 10155kg altogether, output to bleaching or the moisture thick slurry 5615kg of machine hand's section, wherein slightly starch 900kg, water and other solubility thing 4715kg.Acidifying workshop section leaf, black liquor to be processed and waste water is 10155kg altogether, and acidization absorbs SO ₂480kg, major part from the calcining workshop section, about 473kg, boiler waste gas replenishes 7kg; Output facet, acidifying, preheating, precipitation operation all have evaporation, mainly finish in latter two operation, and lignin degradation generates water and CO2, emptying CO ₂272kg.Caustic room, among the digestion lime 1287kg, CaO372.6kg, water 823kg, SO ₂18.5kg, Na ₂O72.9kg; The lixiviate discharge quantity is by SO superfluous in the acid clear liquid ₂With solubility CO in the basic clinker ₃ ^-2Between relative quantity determine causticization slag 1689kg, water 844.7kg wherein, CaO372.6kg, Na ₂O66.0kg, SO ₂366.4kg, CO ₂39.3kg.Contain Na in the lixiviate slag ₂O1.63kg, SO ₂1.45kg, water 21.5kg, insoluble matter 20.4kg.In the calcining workshop section, the waste gas effective ingredient refers to SO in the waste gas ₂, CO ₂, Na ₂The summation of O and steam, but disregard steam and the CO that heavy oil combustion produces ₂, in the waste gas, SO ₂(488.0kg wherein nearly 15kg be condensed water absorb take away), steam 997.8kg, CO ₂1229.2kg; Water evaporation is meant the summation of lignin and basic clinker prevapourising moisture before entering burner hearth.On gross mass balance hurdle, the importation shows, except that the energy, only needs timber 3539kg, Na ₂SO ₄16kg, CaCO ₃18kg and water 7905kg just can produce one ton of thick slurry, and alkali recovery is 95%.

The budgetary estimate of table 1. mass balance

Unit: kg

	Input	Output
			Cooking section	Wood chip 1896 wood chip moisture 1643 cooking liquors 5559	Paper pulp 900 black liquor 7039 spurt gas 1043 boilings venting 116
Washing room	Paper pulp 900 black liquor 7039 washings 7905	Black liquor 10155 washing evaporation 74 paper pulp (moisture) 5615
			Acidifying workshop section	Black liquor 10155 absorbs SO 2480 acidifyings suction 50	Acid clear liquid 5890 lignins (moisture) 2453 evaporations 2070 lignin degradations 272
Caustic room	Acid clear liquid 5890 basic clinkers 201 digestion lime 1287	Alkalescence clear liquid 5559 lixiviate slags 45 causticization slags 1689 lixiviates venting CO 235 lixiviate water evaporations 50
			Calcining workshop section	Lignin 2453 causticization slags 1689 replenish Na 2SO 416 replenish CaCO 318 lignin oxygen consumptions 996	Waste gas effective ingredient 2715 basic clinkers 201 lime 468 water evaporations 1788
The gross mass balance	Wood chip 1896 wood chip moisture 1643 washings 7905 replenish Na 2SO 416 replenish CaCO 318 lignin oxygen consumptions, 996 boiler waste gas are for sulphur 7	Spurt gas 1043 boilings venting 116 washing evaporation 74 paper pulp (moisture) 5615 acid precipitations and evaporate 2070 lignin degradations, 272 lixiviate slags, 45 lixiviates venting CO250 lignin burnt gas 1254 are evaporated in 35 lixiviate water evaporations, 50 digestion evaporations, 50 digestion slags, 19 water evaporations, 1788 condensation ponds
			Amount to	????12481	????12481

Claims (5)

1. an acidifying sulfate pulp-making process comprises boiling, washing, acidifying, causticization and five workshop sections of calcining, and wherein boiling, washing room are identical with traditional kraft process or soda pulping process method; Acidifying workshop section is with the SO in the stack gases ₂Make the acidulant of black liquor, and the black liquor after adopting black liquor acidifying pyrolysis sedimentation reaction to acidifying carries out the physical chemistry processing; Caustic room is with the Na in the acid clear liquid with CaO ₂SO ₃Convert NaOH and CaSO to ₃Precipitation is characterized in that: it is main fuel that calcining workshop section adopts heavy oil, and using the lignin of separating from black liquor is auxiliary fuel, in calcining kiln with CaSO ₃Be sintered into CaO and SO ₂, the SO that the calcining back generates ₂Flow back to acidifying workshop section as acidulant, CaO that the calcining back generates and condensed water digestion, digestion lime after separating thick slag is used for caustic room, and the acid clear liquid that acidifying workshop section produces is isolated alkaline clear liquid behind the digestion lime causticization, is used as the cooking liquor of cooking section after dosing.

2. pulp-making method according to claim 1 is characterized in that: the SO that the calcining back produces ₂Send the dedusting operation of acidifying workshop section, basic clinker Na ₂CO ₃Send the lixiviate of caustic room respectively and digest operation with CaO.

3. pulp-making method according to claim 1 and 2 is characterized in that: before the calcining, add an amount of Na ₂SO ₄With the mixed loss of lignin, add The addition of C aCO with Na in the replenishment cycles ₃With CaSO ₃Mixed loss with Ca in the replenishment cycles.

4. pulp-making method according to claim 1 and 2 is characterized in that: the high-temp waste gas that calcining produces carries out heat exchange through heat exchanger and clear water, send the dedusting operation of acidifying workshop section after the waste gas cooling, mainly sends to laundry after the clear water heating and washs workshop section.

5. according to claim 1 or 2 or 4 described pulp-making methods, it is characterized in that: the SO that acidifying is used ₂Mainly take from the stack gases of calcining workshop section, boiler flue waste gas is only as SO ₂Additional source.

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