CN87101508B - Urea process for making paper pulp - Google Patents

Abstract

The present invention relates to an improved industrial papermaking chemical pulping method, particularly to a pulping method for steaming grass raw materials by adopting urea or urea as the main part adding micro auxiliary agents. The method does not use alkali and uses urea with sufficient raw material source as steaming agents, ureolysis has a delignify function under the condition of high temperature and high pressure. Waste liquid in the pulping process has easy biochemical treatment and comprehensive utilization, and waste gas is recycled to save urea dosage. The pulping method of the present invention solves the problems of shortage wanting current pulping chemical raw material alkali and gradually serious pollution, reduces the pulping cost, enhances the economic benefit, and provides irrigation water containing fertilizer for agricultural production.

Description

Urea process for making paper pulp

The present invention relates to a kind of improved industrial paper chemistry pulping process, particularly adopt urea or be the main method that adds trace assistant boiling grass raw pulp with urea.

The traditional chemical pulping process of industrial normal employing mainly contains alkaline process and sulphite process two classes, and with the most use with alkaline process.Mostly China's paper-making industry is alkaline process production, and supply falls short of demand owing to alkali output, and pulping yield is low again, and alkaline consumption is big and can not effectively reclaim, and pollution is on the rise, and has caused some paper mills to stop production.Especially making grass pulp.Because of black liquor ashes height, dioxide-containing silica is many, the easy fouling of the evaporation of black liquor in alkali recovery process, and the difficult clarification of white liquid, and alkali runs off big; The burning of black liquor easily stifled nozzle, the also recovery of unfavorable alkali.Therefore, in that there is lack of raw materials, under the situation of environmental pollution, seriously influenced the development of careless class pulping and papermaking industry.At present both at home and abroad all in research slurrying new technology, the chemical pulping process method of reform traditional.The present inventor once adopted ammoniacal liquor system straw pulp, because ammoniacal liquor is volatile summer, loss is big, and need antifreeze winter, and the ammonia flavor people that chokes is so operating condition is very abominable.Digestion process can not little venting and cause forging and pressing big in addition, and when 150 ℃ of boiling temperatures, pressure is up to 9～10kg/cm ²Therefore, be difficult in actual production, use.Report according to relevant patent documentation: digestant slurrying (US-4178861) was once done with quinone-amine by the U.S.; Also have United States Patent (USP) (US-3368935) to introduce and use sodium sulfite Na ₂O ₃Do digestant, add a small amount of urea adjust pH again and do buffer and come slurrying, what boiling played a major role is not urea; Once using a large amount of urea, sulphur urine (consumption be about wood chip 300～600%) in the U.S. Pat 2361639, is to flood wood chip under 65～107 ℃ the condition in temperature.Because of this temperature is too low, urea does not also decompose, and does not have the effect of delignification, is not boiling under high temperature, the high pressure, can only be dipping under the normal pressure.Although this patent was also once mentioned 137～182 ℃, temperature at this moment is not a dipping temperature, neither boiling temperature, but behind softening wood chip and defibrination, the hot pressing temperature when lamination or compression molding, therefore, urea is not the effect of digestant.In a word, the pulping process of narrating in above-mentioned several documents is mainly used in wood-cellulose slurrying, and is not used in the system straw pulp; Urea is used as buffer, and the dipping softening agent is not to be used as digestant.Therefore, lack at current alkali, seriously polluted, hinder under the situation that slurrying already develops, work out a kind of without alkali, pollution abatement, the pulping process that yield is high has more and more become the problem of people's common concern.

Purpose of the present invention just provides a kind of improved chemical pulping method, and this method need not acid or alkali and do digestant with urea, and not only cost is lower than soda pulping process, and waste liquid is easy to biochemical treatment, and comprehensive utilization reduces the pollution to environment.

The object of the present invention is achieved like this: utilize urea easily to decompose under high temperature, high pressure, urea and catabolite thereof have the effect of delignification, adopt certain amount of urea or be mainly to add trace assistant and do digestant with urea, the blade qualified with processing, be put in the spiral propeller, add aqueous solution of urea and mix, give and soaking, the digesting apparatus of packing into then carries out boiling.In digesting apparatus, feed Steam Heating, during to uniform temperature, carry out little venting, heat up again.Heat up after a period of time, be incubated the stipulated time after the final relief step-down, blowing enters the drip washing pond again, the straw pulp that washing is good removes making beating system paper through pumping.Waste liquid is removed suspended matter through sedimentation basin, defecator sedimentation.Dense waste liquid is received that with blowback heat-accumulator tank is standby; Rare waste liquid is delivered to the stem or leaf of cattail, reed planting field through biochemical treatment or be directly used in the liquid mixing of waste gas in check valve, jet pump and heat-accumulator tank that irrigation, final relief emit and reclaim, and is placed in the heat-accumulator tank standby.This pulping process is lower than soda pulping process cost, and waste liquid, the recyclable effect of waste gas have reduced the pollution to environment, and therefore, it is a kind of effective system straw pulp method of turning harm into good.

The present invention is further described below in conjunction with accompanying drawing.

Fig. 1 is the process flow diagram of urea pulp-making method of the present invention.

Describe concrete technological process of the present invention and method of operating in detail according to Fig. 1.This pulping process serves as that the main trace assistant that adds is done digestant and come the boiling grass to carry out slurrying to produce with urea or with urea.At first dogstail such as straw or wheat straw, cotton stalk are got the raw materials ready routinely, be processed into qualified blade, deliver to spiral propeller 2 through scratch board conveyor 1 then.2 li of spiral propellers, blade and urea add water or add heated effluent that heat-accumulator tank 11 reclaimed and mixes to give and soak, and amount of water (comprising the heated effluent that adds from heat-accumulator tank 11) is 1.2～6 times of blade weight.Wherein amount of urea can be selected for use according to the variety classes of dogstail.As blade is straw, and amount of urea is 3～20% of a straw weight; As blade is cotton stalk or straw, and amount of urea is 4～27% of cotton stalk or a straw weight, also will add trace assistant sulphur or its compound in addition, and auxiliary dosage is 0.01～5% of cotton stalk or a straw weight.Blade is given by urea liquid and soaking in spiral propeller 2, and the digesting apparatus 3 of packing into then carries out boiling.Conditions of cooking is: when digesting apparatus 3 feeding steam intensifications are heated to 80～110 ℃ (be no more than 110 ℃ of urea and can not decomposite ammonia), carry out little venting; Continuing to heat up 35～60 minutes, is 125～180 ℃ in maximum temperature again, and maximal pressure is 4～9kg/cm ²Condition under be incubated 7～0.5 hours.At this moment, urea begins to decompose under high temperature, high pressure, removes the lignin in the blade.Carrying out final relief after being incubated the stipulated time, reduce the pressure in the digesting apparatus 3, is blowing at last, and the straw pulp after the boiling is put into drip washing pond 4.Dense waste liquid in the straw pulp is at first through sedimentation basin 7, defecator 8 sedimentation suspended matters, and it is standby that heavy dense waste liquid after clear is squeezed into heat-accumulator tank 11 by pump 9.The drip washing straw pulp that discharges water again, the straw pulp that washing is good is sent to making beating with pump 10 and is made paper.Drench rare waste liquid of in the drip washing pond 4 again through sedimentation basin 7, defecator 8 sedimentation suspended matters, be used for irrigating.The purification oxidation pond of above-mentioned sedimentation basin 7, the defecator 8 also available plantation stem or leaf of cattail or reed comes the sedimentation suspended matter and reduces biological oxygen demand (BOD) and chemical oxygen consumption (COC), through purifying water base the paper industry standard of drainage that can reach national regulation that oxidation pond is discharged.The waste gas of discharging in digesting apparatus 3 final reliefs contains ammonia, and directly discharging atmosphere pollution influences operating environment.For this reason, with the liquid mixing of waste gas in check valve 5, jet pump 6 and heat-accumulator tank that final relief is discharged, with ammonia and heat recovery, it is standby to put back to heat-accumulator tank again.This gas recovery method is not only eliminated the pollution to environment, and can save amount of urea and reclaim heat.

Urea process for making paper pulp of the present invention is raw materials used to be the sufficient urea in source, its cost is lower than alkali, and is lighter than alkaline process to the corrosion of metal of digesting apparatus, especially through after 140 hours, urea method slurrying does not have corrosiveness substantially to metal, therefore the service life that can improve digesting apparatus.Nitrogen, phosphorus, the easy biochemical treatment of potassium can be directly used in irrigation in the waste liquid, turn bane into boon, and have supported agricultural production.Waste gas is recycled, and can save amount of urea and reclaim heat, has further reduced the slurrying cost.Boiling straw pulp unscreened yield 71.5～76.5%.

The straw pulp of urea method production is joined 30% wood pulp can produce the boxboard that meets China National Light Industrial Products Department's standard-required, and 100% urea method straw pulp can be produced 1# wrapping paper, 1# fluting medium, reaches China National Light Industrial Products Department's standard.Therefore, urea method slurrying had both solved current alkali shortage, and the problem that environmental pollution is serious has reduced the slurrying cost again, has improved economic benefit, can also provide the irrigation water that contains fertilizer for agricultural production.

Claims (2)

1, a kind of urea process for making paper pulp, it is characterized in that adopting urea or be mainly to add trace assistant and do digestant with urea, the blade qualified with processing is put in the spiral propeller, adds aqueous solution of urea and mixes, and gives and soaking, the digesting apparatus of packing into then carries out boiling, when being warmed up to 80～110 ℃, carry out little venting, continue again to heat up 35～60 minutes, in maximum temperature is 125～180 ℃, and maximum pressure is 4～9kg/cm ²Condition under be incubated 7～0.5 hours, final relief after being incubated the stipulated time, blowing is to the drip washing pond, the straw pulp that washing is good is sent to making beating system paper, waste liquid utilizes through sedimentation basin, defecator sedimentation suspended matter again, the liquid mixing of the waste gas that final relief is discharged in check valve, jet pump and heat-accumulator tank reclaims, wherein amount of urea is 3～20% of a straw blade weight, or based on the urea of cotton stalk, straw blade weight 4～27%, add 0.01～5% auxiliary agent sulphur or its compound, amount of water is 1.2～6 times of blade weight.

2, pulping process according to claim 1 is characterized in that the sedimentation basin of waste liquid process, defecator can replace with the purification oxygen pool of the plantation stem or leaf of cattail or reed.

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