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YueWenYuan

(kumho engineering technology co., LTD. Kunshan, jiangsu province, 215300)

Abstract: the Vacuum Pressure Adsorption (Vacuum Pressure Swing Adsorption, VPSA) system, namely the psa oxygen generator, convenient operation, simple maintenance, less investment, low operating cost, for the pulp enterprises in domestic market spread. This paper introduces the characteristics of the equipment and its application in pulp bleaching.

Key words: oxygen bleaching; Psa oxygen generator; VPSA; The environmental protection

China classification number: TS737 literature identification code: B article number: 1001-6309 (2006) 03-0024-03

1 oxygen bleaching is clean production technology

With no chlorine bleach (TCF) or no element chlorine bleaching (ECF) instead of CEH three sections of bleaching, solution to pulp and paper industry is one of the cleaner production technology of environmental pollution.

Oxygen bleaching become necessary process segment of develop clean bleaching process, due to oxygen non-toxic, itself has no pollution to the environment, after oxygen to take off the wood, in the back of the bleach and bleaching waste water quantity can be reduced by 50%. In recent years, in view of the requirement of environmental protection, increasing domestic interest in oxygen bleaching. The Swedish government off the oxygen lignin as a new bleaching pulp mill a measures of pollution control. Has been proved that oxygen bleaching can greatly reduce the BOD and COD in the bleaching effluent color degree and total content of organochlorine, it to reduce the pollution of modern pulp bleaching waste water plays an important role. Oxygen bleaching can also save the consumption of other chemicals, compared with chlorine bleach bleached pulp, can increase the pulp yield. Oxygen bleaching liquid can be used for the black liquor extraction, into the alkali recovery system, or a sequence of section after the merger to wastewater treatment in general.

The application of two domestic pulp enterprise oxygen generation equipment are studied

Domestic oxygen bleaching process by the 1990 s to a large number of applications. Only small initial oxygen source choice air cryogenic equipment, advanced technological process for medium voltage crout with turbine expander cycle. From the air inhaled air compressor, air is compressed to the required pressure, then through the cooler junior level at the end of the freon, precooling unit is cooled to 35 ℃ or so into the purification device, in which to remove moisture, carbon dioxide, hydrocarbon and other substances, enter the fractionating column. After purification of compressed air into the fractionating column (on) the main heat exchanger, and the main heat exchanger (below) to gas after heat exchange of oxygen and nitrogen fractions by the confluence of throttle valve with expander out cold air Below the bottom of the evaporator, the tower is heat transfer, mass transfer process. Air next tower preassigned, then on the throttle to further fractionation tower, at the top of the tower to get pure nitrogen, upper tower of the recycled cold draw out the fraction of gas in the heat exchanger Use as a clarifier regeneration after cook a cold, products of pure nitrogen gas through the pipeline to the user. Product oxygen in oxygen tube road after water seal device import storage airbag to oxygen compressor.

Small cryogenic air separation form a complete set of high pressure oxygen compressor and pump station as standard, high investment, high energy consumption, large amount of operating maintenance, typically over ten hours driving time, operation cycle 6 to 12 months. Cryogenic equipment technology more advanced, the greater the energy consumption is lower, and the mill scale is not large with oxygen. For pulp enterprises, for bleaching auxiliary equipment, air separation equipment, stop the inconvenience operation maintenance cost is high, the oxygen source selection is not ideal.

At present domestic largest cryogenic equipment for the pulp bleaching is sea, pulp paper industry co., LTD., hainan KDON (Ar) - 60 - / - 2770/3200 type air separation equipment, oxygen production 2770 nm3 / h, 2004. Choose cryogenic equipment, annual output of 1 million t the size of the bleached pulp, in addition to apply local gas Hugh market blank, there is a lot of demand for oxygen, nitrogen, argon is the main reason.

China's legal system pressure swing adsorption (psa) oxygen research began in the early 1970 s, until the 1990 s realized the industrialization of small devices. Psa oxygen generating is the basic principle of using nitrogen and oxygen in the air on the zeolite molecular sieves (ZMS) with different pressure difference for separation of oxygen and nitrogen adsorption performance.

Initial PSA oxygen generator used for domestic pulp bleaching for pressurized adsorption (PSA) type of small equipment, production under 100 Nm3 / h, power consumption and small cryogenic, about 1.0 1.3 kWh/Nm3 and process is not mature, most of the experimental equipment. Yield and the purity can't long-term stability, performance and loading process is unqualified, molecular sieve has a tendency to powder in the product gas, most of the equipment are not used or not so long, affects the oxygen bleaching in the promotion of domestic paper industry.

VPSA process is adopted widely in foreign advanced psa oxygen generation process. Domestic formal into the industrial application is in the late 1990 s, and quickly applied in the field of domestic paper pulp bleaching. The oxygen purity 93%, can fully meet the requirements of pulp bleaching process, the energy consumption of 0.4 ~ 0.5 kWh/Nm3, with the low pressure large cryogenic air separation, as long as a few minutes drive time, can open parking at any time, no matter in equipment investment and operation cost has a strong competitiveness.

Sfa paper co., LTD., is domestic first USES the ECF four element chlorine bleaching process of pulping enterprises, the production of paper pulp with high whiteness, cleanliness, green environmental protection, etc. Adopt Finland AHLSTROM three sections of pressure screen, oxygen lignin and four Duan Piao technology, supporting VPSAO - 360 type pressure swing adsorption oxygen generator, annual output of 10 t wood pulp bleaching.

Sichuan sinopac paper co., LTD. No chlorine bleaching pulping production line, annual pulp capacity of 80000 t, bamboo pulp devoid of chlorine were white, supporting VPSAO - 260 type pressure swing adsorption oxygen generator is VPSAO - 210 type.

Currently the nation's largest used in pulp bleaching are of variable pressure absorbing oxygen generation equipment are shandong asia-pacific sen bo pulp paper co., LTD., the annual output of 220000 t bleached sulphate wood pulp matching VPSAO - 700 type pressure swing adsorption oxygen generator.

At present domestic straw proportion is very big, but the oxygen bleaching in the application of straw or blank. For oxygen straw lignin, is technically feasible, but the economy is reasonable. Because of the low straw lignin content, oxygen bleaching of wheat straw has better selectivity, high viscosity pulp, good strength, more easily than wood pulp TCF bleaching. Using the factory now drop streaming alkali treatment or hypochlorite bleaching towers, only increase a small amount of auxiliary equipment, can be implemented, to our country traditional bleaching technology transformation and reduce environmental pollution has important practical significance.

Three oxygen bleaching with VPSA oxygen equipment is introduced

VPSA oxygen generation system is mainly composed of blower, vacuum pump, switching valve, of adsorber and oxygen buffer tank. Air via suction mouth after the filter to remove dust particles, roots blower pressurization to 30-50 kpa and enter one of the adsorber. Adsorber fill the adsorbent, including moisture, carbon dioxide and a small amount of other gas composition at the entrance of adsorber is filled in the upper part of the activated alumina adsorption by zeolite molecular sieve. ) of argon and oxygen (including the components as a product from the top of the adsorber the exit gas adsorption to the oxygen buffer tank. When the adsorber adsorption to a certain extent, the adsorbent will reach saturated state, this time by switching valve using the vacuum pump for the vacuum adsorption in the opposite direction (and), vacuum degree is 65-75 kpa. Have adsorption of water, carbon dioxide, nitrogen, and a few other gas composition pumped out to the atmosphere, side by side to the regeneration of adsorbent. VPSA alternate with each adsorber adsorption - desorption - stamping step. The three basic steps process by PLC and switching valve system to realize automatic control.

VPSA oxygen generating device has the advantages of simple process, less equipment, less capital cost, the factory request is not high also, capital cost of equipment with a total investment of 5% ~ 10%.

VPSA device can depend on no-load running, and after parking, mood stable adsorption tower, after driving for a few minutes to a product. Start simple and stop to avoid peak operation, reduce the production cost.

VPSA device itself is simple, operating machinery quantity is little, moving equipment for roots blower and roots vacuum pump, because of its working principle is displacement, oil-free, operating under atmospheric pressure, less maintenance workload, cost is low. Years equipment drive rate is about 98%, and 50% because the fault parking, if less cooling supply failure and power failures, etc. Parking equipment regular maintenance about 5 d per year, due to the air blower vacuum pump oil, moving equipment regular maintenance and operating personnel responsible for non-woven regular replacement of air filters for a period (1-2 months), etc. More than 10 a service life of molecular sieve, switching valve seat is 2-3 a to replace the commonly, vacuum pump bearing and oil seal under normal conditions of use for 3-5 a life.

4 is cheap applicable oxygen source VPSA oxygen generation equipment are studied

VPSA oxygen equipment technology mature, at present, the domestic two tower process level has the international synchronization, average energy consumption of 0.4-0.5 kW. H/Nm3, purity 91% ~ 91%, and all seemed to control, the unit cost of oxygen around 0.4 RMB/Nm3 (local electricity price differences) and oxygen unit price for the market at present about 1 yuan/Nm3.

Cryogenic air separation is the sixth generation of the current domestic most advanced products, in addition to using the structured packing tower and rectification argon outside the two core technology, and application of efficient internal compression process of liquid pressurization turbine expander, high pressure, large cross-section In specifications plate heat exchanger and cold molecular sieve purification technology, such as air separation plant oxygen extraction rate reached 97% 99%, argon extraction rate reached 75% 88%, oxygen consumption down to 0.40-0.42 kW. H/Nm3 but automation control, stay in the mid - 1980 - s level and equipment production is in commonly 6000 Nm - 3. H - 1 above, the current domestic mill scale are not applicable.

Cryogenic preparation can produce oxygen and nitrogen commonly two kinds of products, pulp enterprises is nitrogen gas gap, and the dosage is not big, if transportation sales, market competitiveness is not strong, most of them are empty waste. Oxygen production adjustment is more difficult, adjust time to 1 h, pump configuration platform, yield is not big, market economy.

Processing raw materials oxygen in the air and can not be extracted completely. PSA pressurized adsorption oxygen generator, the raw material air pressure 0.4 Mpa for making oxygen adsorption first, then by atmospheric vent desorption. Characterized by low molecular sieve requirements, equipment is relatively simple, but the energy consumption is higher. The general yield under 100 nm3 / h, more economy. Because of its high product outlet pressure, the more pure oxygen aeration used in sewage, oxygen-enriched aquaculture and other fields.

At present domestic pulping enterprise scale in hundreds of cubic meters with oxygen, oxygen bleaching pulp pressure generally is 0.8 Mpa. VPSA, variable pressure absorbing oxygen generation equipment are low-pressure adsorption oxygen generation, vacuum desorption, oxygen product according to customer's need to configure the pressurized oxygen compressor, again to send users to use, low energy consumption, pulping enterprise configuration is more economic.
 

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