Precipitation of calcium carbonate as an important energy-consuming process, analysis of the control factors of the drying process, design of a reasonable process control process, configuration, optimization of hardware and software systems, friendly man-machine interface, to achieve stable dryer operation, stable dry quality, to achieve Save energy and reduce consumption. The drying control unit can be integrated with the plant control system to form a distributed control system to improve the production efficiency of the system.
I. Overview According to preliminary statistics in the industry, the annual domestic production capacity of precipitated calcium carbonate from the end of the last century to the beginning of this century has reached more than 8 million tons. Under the guidance of industry associations, various domestic manufacturers have continuously popularized calcium carbonate production technology, and the production technology level has been continuously improved. The scale and high efficiency technology has been promoted. Each manufacturer has competed in various aspects such as product variety, quality, production capacity and cost. The industry develops in an orderly manner, and enterprises learn from each other to promote the development of light calcium carbonate production technology. The production process technology and the extensive exchange of various types of talents have made the development of light calcium carbonate leaps and bounds.
Calcium carbonate has been deeply developed and applied in the chemical, pharmaceutical, building materials, papermaking and other industries, and has become an important inorganic chemical raw material in the national economy.
Most of the production of precipitated calcium carbonate is formed by carbonization after lime digestion. The principle is the same, but the process is different, and the effect is also obviously different. The carbonized water mixture is filtered to form a wet filter material having unequal water content. Wet filter media must be dried to remove moisture to produce a desired calcium carbonate product.
Drying is usually achieved by heating the semi-finished material with a heat medium to evaporate the water, which is a process that consumes heat.
In the cost of calcium carbonate, the cost of energy consumption accounts for more than 80% of the total cost, while the cost of drying energy consumption for wet filter materials accounts for more than 40% of the total cost. Therefore, the cost of drying directly affects the cost of the product. Increasing the production capacity of drying equipment, improving the process control technology level of the equipment, and stabilizing the drying conditions are the main ways to reduce the energy consumption and cost of drying.
2. Overview of drying equipment At present, the drying equipment used by various production enterprises mainly includes drum type tube type, disc type, paddle type, hot air strong drying type. Different types of drying equipment can be used depending on the nature of the wet filter material and the moisture content. For light calcium, most manufacturers use roller tube drying equipment.
In recent years, HYGL series roller tube dryers produced by Hongyu Company have been recognized by users in light calcium drying production. This series of products is a new product independently researched and developed by the company, relying on technological innovation and based on the original technology. The product is mainly composed of a cylinder body, a large-area inner heating tube bundle, an outer heating coating tube, a rolling ring, a supporting wheel, a retaining wheel, a transmission mechanism and auxiliary components. The heating medium may be medium or low pressure steam, or may be an organic heat carrier, that is, a heat transfer oil. Use temperature range 220---300 °C, pressure range 0.4---1.2Mpa.
The heating medium enters the large-area pipe and the barrel pipe through the rotary joint to release heat, and the material enters through the material inlet. When the unit rotates, the material absorbs heat through heat conduction and evaporation convection, and the material and the moisture are heated and continuously evaporation. The evaporated water vapor is taken out in time to reduce the evaporation surface pressure, and maintaining the micro-negative pressure in the evaporator evaporation cylinder can promote the evaporation process. Due to the continuous rotation of the cylinder, the evaporation surface of the internal material changes continuously under the action of the plate, which strengthens the evaporation process.
HYGL series dryer adopts large-row tube heat exchange, large heat transfer area, high heat exchange efficiency, drying capacity per unit volume is more than 3 times that of conventional dryer, and the unit thermal efficiency reaches 90%. Due to the reasonable structure, the heat exchange between the material and the heat medium in the dryer is reasonable, the logistics is smooth, the uniformity of drying is good, the operability is strong, the maintenance is easy, and the operation is stable.
Third, the automatic control process scheme of the drum tube dryer adopts the automatic control technology which is widely used and mature in performance, and the drying equipment can achieve the goal of stable operation, energy saving and consumption reduction. The relevant content is now introduced as follows.
Single-stage automatic control scheme for 35,000 tons of light calcium drum tube dryer 1. Process parameters (1) Precipitated calcium carbonate paste with water content less than 32%. Feeding temperature: 25～30°C
Feeding amount: 6-8 tons / hour discharge moisture content: 0.3%
(2) Heating steam temperature: 260 ± 5 ° C
Pressure: 0.8±0.05MPa
Flow rate: 3~6 tons/hour 2. Process control principle The amount of water discharged from the drum tube dryer is directly related to the discharge temperature and drying evaporation pressure, and has a positive relationship with the feed amount and the drum rotation speed. According to these factors, the discharge temperature is the main control parameter, and the pressure in the dryer is the auxiliary control parameter.
When the discharge temperature deviates from the set value, the regulator outputs a set of signals respectively, and the secondary loop regulator adjusts the steam addition amount; the other sends the drum frequency converter adjusts the drum speed; the third feed feeder adjusts the frequency converter The feeder adjusts the speed of the feeder to adjust the amount of feed. When the discharge temperature rises, the regulator adjusts the steam regulating valve to close the small steam inlet amount, and accordingly increases the feeding amount, and the drum rotation speed also increases correspondingly until the discharge temperature returns to the normal value; when the discharge temperature decreases, the regulator increases the steam supply. Into the amount, the feed amount is appropriately reduced, and the drum rotation speed is correspondingly reduced until the discharge temperature returns to a normal value. When the feed increases or decreases, the rotation speed of the drum is correspondingly increased or decreased to maintain the balance of the feed and discharge.
This disturbance is overcome by sub-ring regulation when the steam pressure changes.
In order to discharge the evaporated water vapor in time and process it, the pressure in the exhaust steam cylinder is taken as the control parameter. When the pressure changes, the pressure transmitter sends the pressure regulator and compares with the given value, and outputs an adjustment signal to control the frequency conversion of the induced draft fan, and the frequency converter controls the motor speed of the induced draft fan to achieve the effect of controlling the pressure inside the exhaust steam cylinder. . The pressure inside the exhaust steam cylinder maintains a slight negative pressure.
The dryer drum motor is interlocked with the feed motor. When the dryer stops due to a fault, the feed motor trips and alarms. The exhaust fan is interlocked with the feed motor. When the exhaust fan is shut down due to a fault, the feed motor trips and alarms. The discharge motor is interlocked with the drum motor. When the discharge motor stops due to a fault, the drum motor trips and alarms.
3. After the initial statistics of automatic control design and equipment selection, determine the number of analog I/O points, digital I/O points, and the number of switches.
Instrumentation thermal workers can make logic control design, terminal equipment and hardware selection according to the above situation.
Software design of the control process, software personnel to evaluate the effectiveness of the dryer control analysis, capture sensitive and effective controllable physical and chemical quantities, control the process and interlock, program control chart formation, generate I / O tables, design Various types of reports and record format tables.
After completing the above tasks, the software personnel configure the relevant equipment and control system, simulate the operation on the machine, and pass the preliminary acceptance of Party A and the supervision organization to form a friendly human-machine interface. After the equipment is delivered, it will be installed on site, commissioned, and accepted by the expert group to form a text report. Prepare manuals for process operations, train relevant operations management personnel, etc. Among them, the combination of designers, process technicians and experienced operators should be implemented in the commissioning phase. That is, the calculation method and the unreasonable program control are corrected by the software designer in the test run; the process technician should cooperate with the software designer to complete the optimization of the control system; the experienced operator proposes the good operation data and the change cycle of each factor. For the process technician to refer to tuning parameters such as PID. And the parameters after setting should be corrected in time as the material characteristics and the characteristics of the heat medium change. Only in this way is it possible to make the control system in a good operating state and to play its due role.
The dryer control unit is formed in combination with the above.
When multiple dryers are running in parallel, DCS control can be realized and integrated with the overall control system of the plant to achieve the goal of centralized monitoring and decentralized control.
4. Analysis of economic benefits and environmental benefits After implementing the automatic control technology of the dryer, the dryer runs smoothly, the product quality is stable, and the heat consumption is reduced. According to relevant data, automatic control is 30% lower than the energy consumed by manual operation. With an annual output of 35,000 tons of light calcium production line, the annual saving of thermal coal is:
3.5 million tons × 90 kg / ton of calcium × 30% / 1000 = 0.094 million tons of discount 0.0945 × 800 yuan / ton = 756,000 yuan.
The investment in a single dryer control system is about 160,000 yuan, and the investment recovery period is:
16/(75.6/11) = 2.32 months. That is, under normal circumstances, the investment can be recovered in less than three months.
Since the amount of coal used is reduced, the amount of emissions is naturally reduced, and the single machine can save more than 700,000 yuan per year.
The dryer control process plan is as follows:
IV. Conclusion The HYGL roller tube dryer is equipped with automatic control of temperature, feeding and discharging, which can achieve the goal of stabilizing the operation of the dryer, ensuring product quality and reducing energy consumption. The project not only has good economic benefits but also has good environmental benefits, and is worthy of promotion and application among the majority of users.
I. Overview According to preliminary statistics in the industry, the annual domestic production capacity of precipitated calcium carbonate from the end of the last century to the beginning of this century has reached more than 8 million tons. Under the guidance of industry associations, various domestic manufacturers have continuously popularized calcium carbonate production technology, and the production technology level has been continuously improved. The scale and high efficiency technology has been promoted. Each manufacturer has competed in various aspects such as product variety, quality, production capacity and cost. The industry develops in an orderly manner, and enterprises learn from each other to promote the development of light calcium carbonate production technology. The production process technology and the extensive exchange of various types of talents have made the development of light calcium carbonate leaps and bounds.
Calcium carbonate has been deeply developed and applied in the chemical, pharmaceutical, building materials, papermaking and other industries, and has become an important inorganic chemical raw material in the national economy.
Most of the production of precipitated calcium carbonate is formed by carbonization after lime digestion. The principle is the same, but the process is different, and the effect is also obviously different. The carbonized water mixture is filtered to form a wet filter material having unequal water content. Wet filter media must be dried to remove moisture to produce a desired calcium carbonate product.
Drying is usually achieved by heating the semi-finished material with a heat medium to evaporate the water, which is a process that consumes heat.
In the cost of calcium carbonate, the cost of energy consumption accounts for more than 80% of the total cost, while the cost of drying energy consumption for wet filter materials accounts for more than 40% of the total cost. Therefore, the cost of drying directly affects the cost of the product. Increasing the production capacity of drying equipment, improving the process control technology level of the equipment, and stabilizing the drying conditions are the main ways to reduce the energy consumption and cost of drying.
2. Overview of drying equipment At present, the drying equipment used by various production enterprises mainly includes drum type tube type, disc type, paddle type, hot air strong drying type. Different types of drying equipment can be used depending on the nature of the wet filter material and the moisture content. For light calcium, most manufacturers use roller tube drying equipment.
In recent years, HYGL series roller tube dryers produced by Hongyu Company have been recognized by users in light calcium drying production. This series of products is a new product independently researched and developed by the company, relying on technological innovation and based on the original technology. The product is mainly composed of a cylinder body, a large-area inner heating tube bundle, an outer heating coating tube, a rolling ring, a supporting wheel, a retaining wheel, a transmission mechanism and auxiliary components. The heating medium may be medium or low pressure steam, or may be an organic heat carrier, that is, a heat transfer oil. Use temperature range 220---300 °C, pressure range 0.4---1.2Mpa.
The heating medium enters the large-area pipe and the barrel pipe through the rotary joint to release heat, and the material enters through the material inlet. When the unit rotates, the material absorbs heat through heat conduction and evaporation convection, and the material and the moisture are heated and continuously evaporation. The evaporated water vapor is taken out in time to reduce the evaporation surface pressure, and maintaining the micro-negative pressure in the evaporator evaporation cylinder can promote the evaporation process. Due to the continuous rotation of the cylinder, the evaporation surface of the internal material changes continuously under the action of the plate, which strengthens the evaporation process.
HYGL series dryer adopts large-row tube heat exchange, large heat transfer area, high heat exchange efficiency, drying capacity per unit volume is more than 3 times that of conventional dryer, and the unit thermal efficiency reaches 90%. Due to the reasonable structure, the heat exchange between the material and the heat medium in the dryer is reasonable, the logistics is smooth, the uniformity of drying is good, the operability is strong, the maintenance is easy, and the operation is stable.
Third, the automatic control process scheme of the drum tube dryer adopts the automatic control technology which is widely used and mature in performance, and the drying equipment can achieve the goal of stable operation, energy saving and consumption reduction. The relevant content is now introduced as follows.
Single-stage automatic control scheme for 35,000 tons of light calcium drum tube dryer 1. Process parameters (1) Precipitated calcium carbonate paste with water content less than 32%. Feeding temperature: 25～30°C
Feeding amount: 6-8 tons / hour discharge moisture content: 0.3%
(2) Heating steam temperature: 260 ± 5 ° C
Pressure: 0.8±0.05MPa
Flow rate: 3~6 tons/hour 2. Process control principle The amount of water discharged from the drum tube dryer is directly related to the discharge temperature and drying evaporation pressure, and has a positive relationship with the feed amount and the drum rotation speed. According to these factors, the discharge temperature is the main control parameter, and the pressure in the dryer is the auxiliary control parameter.
When the discharge temperature deviates from the set value, the regulator outputs a set of signals respectively, and the secondary loop regulator adjusts the steam addition amount; the other sends the drum frequency converter adjusts the drum speed; the third feed feeder adjusts the frequency converter The feeder adjusts the speed of the feeder to adjust the amount of feed. When the discharge temperature rises, the regulator adjusts the steam regulating valve to close the small steam inlet amount, and accordingly increases the feeding amount, and the drum rotation speed also increases correspondingly until the discharge temperature returns to the normal value; when the discharge temperature decreases, the regulator increases the steam supply. Into the amount, the feed amount is appropriately reduced, and the drum rotation speed is correspondingly reduced until the discharge temperature returns to a normal value. When the feed increases or decreases, the rotation speed of the drum is correspondingly increased or decreased to maintain the balance of the feed and discharge.
This disturbance is overcome by sub-ring regulation when the steam pressure changes.
In order to discharge the evaporated water vapor in time and process it, the pressure in the exhaust steam cylinder is taken as the control parameter. When the pressure changes, the pressure transmitter sends the pressure regulator and compares with the given value, and outputs an adjustment signal to control the frequency conversion of the induced draft fan, and the frequency converter controls the motor speed of the induced draft fan to achieve the effect of controlling the pressure inside the exhaust steam cylinder. . The pressure inside the exhaust steam cylinder maintains a slight negative pressure.
The dryer drum motor is interlocked with the feed motor. When the dryer stops due to a fault, the feed motor trips and alarms. The exhaust fan is interlocked with the feed motor. When the exhaust fan is shut down due to a fault, the feed motor trips and alarms. The discharge motor is interlocked with the drum motor. When the discharge motor stops due to a fault, the drum motor trips and alarms.
3. After the initial statistics of automatic control design and equipment selection, determine the number of analog I/O points, digital I/O points, and the number of switches.
Instrumentation thermal workers can make logic control design, terminal equipment and hardware selection according to the above situation.
Software design of the control process, software personnel to evaluate the effectiveness of the dryer control analysis, capture sensitive and effective controllable physical and chemical quantities, control the process and interlock, program control chart formation, generate I / O tables, design Various types of reports and record format tables.
After completing the above tasks, the software personnel configure the relevant equipment and control system, simulate the operation on the machine, and pass the preliminary acceptance of Party A and the supervision organization to form a friendly human-machine interface. After the equipment is delivered, it will be installed on site, commissioned, and accepted by the expert group to form a text report. Prepare manuals for process operations, train relevant operations management personnel, etc. Among them, the combination of designers, process technicians and experienced operators should be implemented in the commissioning phase. That is, the calculation method and the unreasonable program control are corrected by the software designer in the test run; the process technician should cooperate with the software designer to complete the optimization of the control system; the experienced operator proposes the good operation data and the change cycle of each factor. For the process technician to refer to tuning parameters such as PID. And the parameters after setting should be corrected in time as the material characteristics and the characteristics of the heat medium change. Only in this way is it possible to make the control system in a good operating state and to play its due role.
The dryer control unit is formed in combination with the above.
When multiple dryers are running in parallel, DCS control can be realized and integrated with the overall control system of the plant to achieve the goal of centralized monitoring and decentralized control.
4. Analysis of economic benefits and environmental benefits After implementing the automatic control technology of the dryer, the dryer runs smoothly, the product quality is stable, and the heat consumption is reduced. According to relevant data, automatic control is 30% lower than the energy consumed by manual operation. With an annual output of 35,000 tons of light calcium production line, the annual saving of thermal coal is:
3.5 million tons × 90 kg / ton of calcium × 30% / 1000 = 0.094 million tons of discount 0.0945 × 800 yuan / ton = 756,000 yuan.
The investment in a single dryer control system is about 160,000 yuan, and the investment recovery period is:
16/(75.6/11) = 2.32 months. That is, under normal circumstances, the investment can be recovered in less than three months.
Since the amount of coal used is reduced, the amount of emissions is naturally reduced, and the single machine can save more than 700,000 yuan per year.
The dryer control process plan is as follows:
IV. Conclusion The HYGL roller tube dryer is equipped with automatic control of temperature, feeding and discharging, which can achieve the goal of stabilizing the operation of the dryer, ensuring product quality and reducing energy consumption. The project not only has good economic benefits but also has good environmental benefits, and is worthy of promotion and application among the majority of users.
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