Take these measures to solve the problem of contin

2022-08-01
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Take these measures to solve the problem of continuous steaming system

release date: Source: technical editor of pulp and paper: number of views of the package: 2191 copyright and disclaimer

core tip: a 150t/d continuous cooking and pulping production line of a paper company in Shandong uses alkali cooking process with wheat straw as the main raw material. The production process consists of dry preparation, wet preparation and continuous cooking

[China Packaging News] a 150t/d continuous cooking and pulping production line of a paper company in Shandong uses wheat straw as the main raw material and adopts the alkali cooking process. The production process consists of three parts: dry preparation, wet preparation and continuous cooking. After the technical transformation for a series of problems occurred in the operation of the equipment, the quality is stable, and the average daily output exceeds the original design capacity (the maximum daily output reaches 180t)

after the project has been put into operation for a period of time, the production capacity has not met the design requirements, there are many equipment failures, sudden problems often occur, the startup rate is low, the quality of crude pulp is unstable, the pulp is difficult to wash, the amount of screened pulp is large, and the yield is low. In order to improve the production capacity and quality, all parts of the production are comprehensively analyzed, and the problems are found and solved one by one, so as to achieve the optimal configuration of the whole system

1 dry material preparation

(1) the single machine efficiency of the grass cutter (12t/h) is low and requires a lot of personnel. With the passage of time, the feeding personnel are prone to fatigue, resulting in intermittent and uneven thickness of grass supply by the mower, resulting in unstable load of the mower and large fluctuations in the material level of the silo due to the variable hardness of the standard surface and the back

improvement measures: the original 4 sets of 12t/h grass cutters were transformed into 2 sets of 24t/h grass cutters, and the overall grass cutting efficiency was increased by 50%, ensuring the supply of raw materials for continuous steaming. At the same time, in order to overcome the problem of uneven grass feeding caused by the influence of physical strength on the amount of artificial grass, another important continuity feature of the introduction of automatic small aluminum is its regeneration and circulation ability, which improves the grass feeding efficiency. The 24t/h grass cutter can achieve continuous and stable operation, alleviate the phenomenon that the grass loading load changes from large to small, reduce equipment failures and improve the startup rate

(2) it is difficult to replace the screen plate of double roll dust collector and the replacement cycle is long. If the sieve plate is not replaced in time, it will cause poor dust removal effect or large loss of grass in the dust removal grass foam

improvement measures: in order to replace the sieve plate in time when the grass quality changes and reduce the downtime, the fixation method of the sieve plate of the double roll dust collector is changed from the original bolt fixation to the drawer type. This scheme not only reduces the labor intensity, but also improves the labor efficiency. The screen hole of the dust collector is changed in time with the change of grass quality, which not only ensures the dust removal efficiency, but also reduces the loss of grass

(3) in actual production, there are many sliding parts of the rotating parts of the silo, which are prone to failure due to the poor operating environment of the equipment

improvement measures: in order to avoid the shutdown of the whole production line due to silo failure, a belt conveyor is added at the upper part of the silo to directly connect the feed inlet of the silo to the discharge outlet. When the silo needs to be shut down for maintenance due to failure, switch to the top conveyor in time to ensure continuous steam operation. Insufficient: the buffer function of the silo disappears, and the feeding amount of the cooking system cannot be adjusted flexibly, but it buys time for maintenance and ensures the startup and operation time of the whole production line

2 wet material preparation

(1) the sieve holes on the sieve plate of the hydraulic straw crusher are small and dense. Firstly, it will affect the passing amount of grass, and secondly, the sieve plate is easy to deform and fall off due to large pressure

improvement measures: in order to ensure the carrying capacity of the hydraulic grass crusher, the original opening method on the screen plate of the hydraulic grass crusher was modified from the original dense small holes to sparse large holes, which improved the grass leakage rate of the screen plate and ensured the throughput per unit time

(2) the grass supply quantity of the grass pump fluctuates greatly due to the influence of the grass concentration in the hydraulic grass crusher

improvement measures: in order to improve the stability of grass supply and mitigate the impact of the change of grass concentration in the hydraulic grass crusher on the amount of grass feeding, which has been successfully utilized in the implementation of the "first set" of major equipment, the original two 450m3/h pumps were replaced with 600m3/h, ensuring the feeding volume of the inclined screw and the return screw, and paving the way for the improvement of production capacity

(3) the rotary universal joint of the inclined screw dehydrator is seriously worn, with short operation time, frequent replacement, and sometimes sudden fracture, resulting in damage to the reducer housing

improvement measures: in view of the easy damage of the universal joint of the inclined screw dehydrator, during the first transformation, the internal reversing node of the universal joint was changed from a simple sliding contact to a needle bearing structure, and the service life of the universal joint was extended from one month to three months, but there was still a problem of high noise. The second technical transformation is the direct connection between the reducer and the screw shaft, which greatly reduces the noise and makes the operation more stable

3 cooking

(1) abnormal phenomena such as backflow and slipping often occur during feeding of feeder equipment, which affects the stable operation of the equipment and operation safety

improvement measures: analyzed and determined the factors restricting production: poor dehydration of grass; Excessive wear of screw shaft and anti-skid strip; The feeder belt is loose; The qualified rate of grass cutting is low. In order to reduce the moisture content of the grass in the feeder, a leakage sieve plate is added at the bottom of the pre steaming screw conveyor, and the opening is as large as possible when the strength allows; Summarize the production experience, regularly replace the screw shaft and anti-skid strip, and ensure that the feeder is always in a high-efficiency and stable state; Check the belt of the feeder during each shutdown; Strengthen the inspection of the qualified rate of incoming materials, and immediately notify the material preparation personnel to replace the grass cutting blade when the qualified rate of grass is found to be decreased

(2) when the feeding amount of the feeder is large, the cooking quality is unstable, the raw meal is large and the yield is low; Sometimes, the local filling coefficient in the cooking pipe is too large, the air flow is not smooth, the pressure difference is large, or the pushing torque is large, resulting in the "shaft shifting" of the cooking pipe

improvement measures: in order to save investment in the new project, three cooking pipes are used. At present, after the feeding amount of the feeder becomes larger, the phenomenon of non-uniform evaporation occurs. There are many raw materials, and there are many slags discharged in the washing and screening section, resulting in a decline in the pulp yield. In order to improve the cooking efficiency, a new cooking tube is added, which is changed from the original three tubes to four tubes. After the transformation, high liquid ratio cooking is adopted to increase the rotating speed of the cooking pipe, ensure smooth air flow, and eliminate the phenomenon of "shaft shifting" caused by excessive filling coefficient. After operation, it was found that the alkali consumption of cooking decreased by 10%, the quality of cooking pulp was also significantly improved, the crude residue rate decreased to less than 3.5%, and the pulp yield was significantly improved

(3) when the unloader agitator operates under high temperature and pressure, black liquor leakage often occurs. When large metal foreign matters fall, the rotor is easy to get stuck and cause damage to the reducer gear. After the shutdown reducer is removed, the rotor will be affected by the slurry spraying to help it achieve the two most important goals at present - improving fuel utilization. The mixing wing will slowly shift to the vicinity of the nozzle of the spraying pipe, affecting the spraying

improvement measures: change the operation mode of the unloader, dismantle the original internal mixer as a whole, and transform the outlet discharge pipeline. A is the blowdown valve, B is the ball valve added to the blowdown pipeline (using the characteristics of quick opening and quick closing), and C is the high-pressure black liquor valve. Under normal conditions, valve B is normally open and valve C is normally closed. When the spraying is not smooth, valve C can be opened and valve B can be closed. After 10 ~ 20s, valve B can be opened to see if the liquid level in the unloader drops. If it does, close valve C and continue to start the machine; If it does not lower, continue to close valve B, and then carry out backflushing for many times until it can be flushed. If it is invalid to open and close valve B for many times, switch to the standby blowdown valve to ensure normal production, and then continue to recoil. When the boiler is shut down for maintenance, the pressure of the cooking pipe shall be relieved and drained before manual cleaning

after the transformation, not only the maintenance cost is reduced, but also a motor and its operation cost are saved. The practice shows that the operation effect is good

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