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(11) | EP 3 705 623 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | PULPING METHOD FOR HOUSEHOLD PAPER |
FIELD
BACKGROUND
[0002] In recent years, the industry of household paper has developed expeditiously and the production capacity has increased dramatically. In December 2017, the output of household paper in China already reached 12.957 million tons. Due to surge of production capacity and raw material prices, the competition becomes exceptionally intensive and the whole industry steps into a low-margin era. However, in current household paper pulping process, the pulping system usually employs a cyclic pulping process, each pulping cycle lasting for 13 to 17 minutes. One pulping cycle includes a water adding stage, a feeding stage, a beating stage, and a pumping stage. During the entire process, the pulper and the white-water pump operate at a constant speed, resulting in electrical energy waste in the pulping process.
SUMMARY
[0003] An objective of the present disclosure is to provide a pulping method for household paper so as to overcome the issue of electrical energy waste existing in conventional pulping processes.
[0004] To achieve the objective above, the present disclosure provides the following technical solution: a pulping method of a pulping system for household paper, wherein the pulping system comprises: a pulper, a white-water pump, a roller conveyor, a chain scraper conveyor, and a pulp discharging pump, the pulping method sequentially comprising steps of:
Step 1: adding water: adding water into the pulper via a white-water pump, wherein the operating frequency of the white-water pump is 50∼60Hz, and the duration of water adding is 1∼2 minutes, and the operating frequency of the pulper is 15∼20Hz;
Step 2: feeding: conveying wood pulp to the water-added pulper in step 1 via the roller conveyor and the chain scraper conveyor, wherein the feeding duration is 1∼2 minutes, the operating frequency of the white-water pump is 50∼60Hz, and the operating frequency of the pulper is 35∼40Hz;
Step 3: beating: disintegrating and breaking the wood pulp fed in step 2 into pulp, wherein the operating frequency of the white-water pump is 5∼10Hz, the operating frequency of the pulper is 50∼55Hz, and the operating duration of the pulper is 7∼9 minutes;
Step 4: pumping: quickly pumping away the beaten pulp in step 3 via the pulp discharging pump, wherein the operating frequency of the white-water pump is 20∼25Hz, the operating frequency of the pulper is 20∼55Hz, and the operating duration of the pulper is 90∼ 120 seconds;
Step 5: washing: adding, via the white-water pump, water into the pulper treated in step 4 to wash, wherein the operating frequency of the white-water pump is 35∼40Hz, the operating frequency of the pulper is 20∼25Hz, and the operating duration of the pulper is 20∼40 seconds.
[0005] Preferably, the pulping system further comprises a variable-frequency speed regulator, which is mounted on both of the pulper and the white-water pump.
[0007] In view of the above, the present disclosure offers the following advantages:
- 1. The pulping method according to the present disclosure comprises stages of adding water, feeding, beating, pumping, and washing, wherein the white-water pump is set to operate at high speed and the pulper operates at low speed because the white-water pump does work while the pulper does not do work in this stage; the white-water pump is set to operate at low speed and the pulper operates at high speed in the pulping stage because the pulper does work while the white-water pump does not do work in this stage; during the pumping stage, neither of the white-water pump and the pulper does work, such that they are both set to operate at low speed. By setting operating frequencies of the white-water pump and the pulper based on different stages of pulping, electrical energy waste caused by high-speed running of white-water pump and pulper in the prior art is eliminated, and production costs are saved. The energy consumed per ton of paper of the pulping system drops by 40%, of which the pulper drops by 25%, while the energy consumed by the white-water pump drops by 79%. Additionally, the electricity power intensity of existing constant-speed pulping systems is 22.6 kilowatt hours per ton of paper, while the electricity power intensity of the pulping method of the present disclosure is 12.5 kilowatt hours per ton of paper; it is seen that the electricity power intensity for pulping drops by 10.1 kilowatt hours per ton of paper. If the output for a single set of pulper is 30,000 tons and the electricity price is 0.6 CNY per kilowatt hour, then the electricity fees saved annually is 30,000 tons ∗ 10.1 kilowatt hours per ton ∗ 0.6 CNY per kilowatt hour = 181,800 CNY; hence, the investment may be recovered in about 10 months. Additionally, the wood pulp is differentiated into long fiber pulp and short fiber pulp, wherein the long fiber pulp is more difficult to be disintegrated than short fiber pulp, such that the operating duration of the pulp is set to 7∼9 min in the beating stage, which enables the pulping quality during the beating stage to satisfy the manufacturing process;
- 2. The feeding stage is a wood pulp feeding stage, arranged between the adding-water stage and the beating stage. Besides, the operating frequency of the white-water pump during the feeding stage is 50∼60Hz, and the operating frequency of the pulper is 35∼40Hz. In this way, it may be guaranteed that the wood pulp can be preliminarily disintegrated during the feeding stage so as to enhance beating efficiency and improve pulp quality; the pulper is washed in the washing stage so as to prepare for a next pulping cycle; as such, the overall pulping efficiency is significantly saved;
- 3. By setting the operating frequency of the pulperto 15∼20Hz, 35∼40Hz, 50∼55Hz, 20∼25Hz, 20∼25Hz, respectively, which enables the pulper to smoothly adjust the operating frequency and reduces faults caused by an over large change of the rotating speed upon operation adjustment, thereby prolonging the overall service life;
- 4. The variable-frequency speed regulator may separately adjust the speeds of the pulper and the white-water pump; it offers a good speed switching effect and thus can ensure stable operation of the pulper and the white-water pump;
- 5. The DCS control system implements full automated control of the frequency-variable speed regulator; no manual work is needed during the whole process to adjust the operating frequency, such that the operating frequency may be automatically varied during different stages of the pulping process, further improving productivity.
DETAILED DESCRIPTION OF EMBODIMENTS
[0008] A pulping method of a pulping system for household paper, wherein the pulping system comprises a pulper, a white-water pump, a roller conveyor, a chain scraper conveyor, and a pulp discharging pump, the pulping method sequentially comprising steps of:
Step 1: adding water: adding water into the pulper via a white-water pump, wherein the operating frequency of the white-water pump is 50∼60Hz, and the duration of water adding is 1∼2 minutes, and the operating frequency of the pulper is 15∼20Hz;
Step 2: feeding: conveying wood pulp to the water-added pulper in step 1 via the roller conveyor and the chain scraper conveyor, wherein the feeding duration is 1∼2 minutes, the operating frequency of the white-water pump is 50∼60Hz, and the operating frequency of the pulper is 35∼40Hz;
Step 3: beating: disintegrating and breaking the wood pulp fed in step 2 into pulp, wherein the operating frequency of the white-water pump is 5∼10Hz, the operating frequency of the pulper is 50∼55Hz, and the operating duration of the pulper is 7∼9 minutes;
Step 4: pumping: quickly pumping away the beaten pulp in step 3 via the pulp discharging pump, wherein the operating frequency of the white-water pump is 20∼25Hz, the operating frequency of the pulper is 20∼55Hz, and the operating duration of the pulper is 90∼ 120 seconds;
Step 5: washing: adding, via the white-water pump, water into the pulper treated in step 4 to wash, wherein the operating frequency of the white-water pump is 35∼40Hz, the operating frequency of the pulper is 20∼25Hz, and the operating duration of the pulper is 20∼40 seconds.
- 1. The pulping method according to the present disclosure comprises comprises stages of adding water, feeding, beating, pumping, and washing, wherein the white-water pump is set to operate at high speed and the pulper operates at low speed because the white-water pump does work while the pulper does not do work in this stage; the white-water pump is set to operate at low speed and the pulper operates at high speed in the pulping stage because the pulper does work while the white-water pump does not do work in this stage; during the pumping stage, neither of the white-water pump and the pulper does work, such that they are both set to operate at low speed. By setting operating frequencies of the white-water pump and the pulper based on different stages of pulping, electrical energy waste caused by high-speed running of white-water pump and pulper in the prior art is eliminated, and production costs are saved. The energy consumed per ton of paper of the pulping system drops by 40%, of which the pulper drops by 25%, while the energy consumed by the white-water pump drops by 79%. Additionally, the electricity power intensity of existing constant-speed pulping systems is 22.6 kilowatt hours per ton of paper, while the electricity power intensity of the pulping method of the present disclosure is 12.5 kilowatt hours per ton of paper; it is seen that the electricity power intensity for pulping drops by 10.1 kilowatt hours per ton of paper. If the output for a single set of pulper is 30,000 tons and the electricity price is 0.6 CNY per kilowatt hour, then the electricity fees saved annually is 30,000 tons ∗ 10.1 kilowatt hours per ton ∗ 0.6 CNY per kilowatt hour = 181,800 CNY; hence, the investment may be recovered in about 10 months. Additionally, the wood pulp is differentiated into long fiber pulp and short fiber pulp, wherein the long fiber pulp is more difficult to be disintegrated than short fiber pulp, such that the operating duration of the pulp is set to 7∼9 min in the beating stage, which enables the pulping quality during the beating stage to satisfy the manufacturing process.
[0009] The feeding stage is a wood pulp feeding stage, arranged between the adding-water stage and the beating stage. Besides, the operating frequency of the white-water pump during the feeding stage is 50∼60Hz, and the operating frequency of the pulper is 35∼40Hz. In this way, it may be guaranteed that the wood pulp can be preliminarily disintegrated during the feeding stage so as to enhance beating efficiency and improve pulp quality; the pulper is washed in the washing stage so as to prepare for a next pulping cycle; as such, the overall pulping efficiency is significantly saved. By setting the operating frequency of the pulper to 15∼20Hz, 35∼40Hz, 50∼55Hz, 20∼25Hz, 20∼25Hz, respectively, which enables the pulper to smoothly adjust the operating frequency and reduces faults caused by an over large change of the rotating speed upon operation adjustment, thereby prolonging the overall service life.
[0010] The pulping system further comprises a variable-frequency speed regulator, which is mounted on both of the pulper and the white-water pump. The variable-frequency speed regulator may separately adjust the speeds of the pulper and the white-water pump; it offers a good speed switching effect and thus can ensure stable operation of the pulper and the white-water pump. Additionally, because the pulper operates with heavy load and load has a characteristic of large fluctuation, the variable-frequency model should select a heavy load variable-frequency with a function of torque vector control so as to satisfy the operating environments such as large current impact, large starting torque, and frequency speed regulation, etc. a DCS control system is connected on the variable-frequency speed regulator. The DCS control system is prior art, which will not be discussed in detail here. The DCS control system implements full automated control of the frequency-variable speed regulator; no manual work is needed during the whole process to adjust the operating frequency, such that the operating frequency may be automatically varied during different stages of the pulping process, further improving productivity.
[0011] Besides the preferred embodiments above, the present disclosure also has other embodiments. Those skilled in the art may make various variations and alternations based on the present disclosure, and such variations and alterations should fall within the scope defined by the appended claims without departing from the spirit of the present disclosure.
Step 1: adding water: adding water into the pulper via a white-water pump, wherein the operating frequency of the white-water pump is 50∼60HZ, and the duration of water adding is 1∼2 minutes, and the operating frequency of the pulper is 15∼20HZ;
Step 2: feeding: conveying wood pulp to the water-added pulper in step 1 via the roller conveyor and the chain scraper conveyor, wherein the feeding duration is 1∼2 minutes, the operating frequency of the white-water pump is 50∼60Hz, and the operating frequency of the pulper is 35∼40Hz;
Step 3: beating: disintegrating and breaking the wood pulp fed in step 2 into pulp, wherein the operating frequency of the white-water pump is 5∼10Hz, the operating frequency of the pulper is 50∼55Hz, and the operating duration of the pulper is 7∼9 minutes;
Step 4: pumping: quickly pumping away the beaten pulp in step 3 via the pulp discharging pump, wherein the operating frequency of the white-water pump is 20∼25Hz, the operating frequency of the pulper is 20∼55Hz, and the operating duration of the pulper is 90∼ 120 seconds;
Step 5: washing: adding, via the white-water pump, water into the pulper treated in step 4 to wash, wherein the operating frequency of the white-water pump is 35∼40Hz, the operating frequency of the pulper is 20∼25Hz, and the operating duration of the pulper is 20∼40 seconds.