Methanol plant and synthetic ammonia plant have great similarities, so the introduction of the conversion and purification part of the dosing can be referred to the "Large-scale ammonia industry Solution", which mainly introduces the dosing process strategies such as coal gasification and methanol synthesis.

Batching strategy for Texaco gasifier

Gasifier batching system mainly includes conventional system, sequence system and SIS safety instrument system, among which SIS safety instrument system is the main difficulty and emphasis.

(1) Conventional ingredients

The conventional feeding system of gasifier is mainly based on simple adjustment, and the measurement characteristics of multiplicity are mainly to ensure safety, such as temperature measurement of gasifier, liquid level measurement of chill chamber, etc., different measurement values can be selected as SP values when dosing. The adjustment of oxygen-coal ratio and load is a more complicated circuit in batching.

(2) Sequential ingredients

The slag collecting and locking bucket system under the quench chamber of gasifier

The essence is a sequential batching, involving the process of charging, slag collection, pressure relief, slag discharge, etc., is an alternating pressure batching system.

(3)SIS safety instrumentation system

Gasifier safety system is divided into two parts: sequence system and safety interlock. The functions of these two parts are independent of each other, but the security interlocking function has a higher priority than the sequential system.

Gasifier safety system is a complete set of safety automatic dosing control system from starting, running to stopping. During the operation of the gasifier, each step, whether manual or automatic, the safety system will continuously monitor the valve position status of the most important valves in the production process, and automatically adjust the main process parameters to achieve the best safe operation of the device under normal or given parameters.

Gasifier SIS system includes sequence system (start, stop, purge sequence) and gasifier safety interlock.

(a) gasifier operation sequence: The task is to enable the gasification plant to operate safely and harmonically. Before performing the driving sequence, check that the relevant conditions are in place.

After completing the relevant steps, oxygen and steam blow-off is established by adjusting the opening of the oxygen and steam proportioning valve, so that the flow rate of coal water slurry and oxygen can reach the set value of driving. When the allowable driving conditions are met and the stability time is greater than 30s, the running button can be pressed to continue the driving sequence. All subsequent steps, up to the pressurization of the gasifier, are carried out automatically without operator intervention.

In the driving sequence, if the execution time of any sequence step that does not require operator intervention exceeds the predetermined time limit, the driving fails and the stopping sequence is triggered. DCS alarm indicates driving failure, and indicates the cause of failure.

(b) gasifier shutdown sequence: Whenever the shutdown activation condition occurs or the manual shutdown button is pressed, the shutdown sequence activation of the gasification unit will be activated. The stopping sequence is one-way and irreversible, and once triggered, continues until the end, even if the conditions that caused the gasification unit to jump during the process have returned to normal.

Since parking can occur under any circumstances, the position of each valve is not fixed at the moment of parking. Therefore, in the first step of the shutdown sequence, in addition to cutting off the furnace material, it is necessary to set the switch position of each interlocking program control valve.

(c) Purging sequence: purging oxygen pipe and coal water slurry pipe purging, follow the principle of blowing oxygen pipe first and then blowing coal water slurry pipe purging, stopping coal water slurry pipe purging and then stopping oxygen pipe purging, during the purging of coal water slurry pipe purging, continue to carry out oxygen pipe purging to prevent coal water slurry backflow into the oxygen pipe. Purging can be repeated as many times as needed.

(d) Safety interlock function: The role of the safety interlock function is to continuously monitor the operating conditions of the device and generate actions to stop the device safely in the event of unsafe conditions to prevent damage to the equipment or casualties. During the feeding period, there are strict time requirements for related actions. The safety system is equipped with a "watchdog" timer that triggers the gasifier to stop if the scheduled action is not completed within the specified time.

Batching strategy for SHELL gasifier

The feeding system of SHELL gasifier mainly includes on-line dosing of grinding coal system, interlocking of gasification process, dosing of SIS safety instrument system (whose requirements are similar to Texaco gasifier) and some complex dosing.

(1) Grinding system online batching

(a) System interlocking parking

The feed system shutdown interlock will be activated under the following process conditions and operations: coal weighing feeder feed flow is low, mill stop, stop button shutdown. After the parking interlock is started, it will automatically stop according to the following steps: belt conveyor stop, coal weighing feeder stop, grinding machine stop.

(b) coal weighing feeder interlock conditions: system interlock stop, coal weighing feeder machine speed is low.

(2) gasification process interlocking

(a) Timing of gasification start-stop

Carbon washing tower outlet pressure is less than 0.5MPa, system initialization, system reset, pulverized coal transport, oxygen timeout. After coal feeding, the delay is 7s, the oxygen flow timer starts to time, the time is 40s, after 40s, the oxygen vent valve is closed, the oxygen cut-off valve is opened, if the valve position is not normal, the gasifier interlock stop action.

(b) Gasification interlocking

Including system initialization, system reset, coal grinding system running coal feeding, gasifier interlock shutdown trigger.

(c) Lock bucket PLC logic program

The lock bucket batching system includes the process of "pressure relief - cleaning - slag discharge - pressure - slag collection". It involves slag water process interlocking, slag tank agitator interlocking, carbon washing tower feed pump interlocking, ash pump interlocking, etc.

(3) Part of the complex batching system description

(a) oxygen-coal ratio batching

Median selection of pulverized coal flow -- the feeder of pulverized coal flow adopts pulverized coal regulating valve or changes the pressure of the supply tank for batching. The median selection loop is designed for the pulverized coal flow, and the median value is used to adjust the pressure of the supply tank or the opening of the pulverized coal regulating valve after the three selections of the pulverized coal flow.

Oxygen flow compensation and purity correction - oxygen flow into the furnace is a key factor affecting the temperature of the gasifier, the accuracy of oxygen flow is particularly important, set the temperature of oxygen flow, pressure compensation, compensation calculated compensation flow and oxygen purity correction, and finally get the oxygen flow for dosing.

Oxygen-coal ratio dosing system - oxygen-coal ratio dosing machine adopts standard ratio function and proportion calculation of internal instrument to ensure the stability of oxygen-coal ratio, oxygen-coal ratio given value through the multiplier to calculate oxygen flow OSP, as the remote set of oxygen circuit, after taking the reciprocal multiplier to calculate the pulverized coal flow, as the remote set of pulverized coal single parameter loop, so as to achieve interactive dosing. When the pulverized coal flow rate changes, the oxygen flow rate is calculated automatically through the oxygen-coal ratio, and the output value is adjusted by PID.

When the oxygen flow rate changes, the corresponding amount of pulverized coal is calculated by automatically batching the oxygen-coal ratio. The pulverized coal flow rate changes according to the oxygen-coal ratio through the output value of the PID-adjusted pulverized coal regulating valve.

(b) gasifier load batching

Gasifier load feeder is designed to prevent gasifier load

Too large, set the load change speed limiter, the load per minute change is limited to a certain range. In order to prevent excessive oxygen, a high-low selector is set in the pulverized coal circuit, and the measured pulverized coal amount is compared with the given load. The higher one is taken as the final value of the pulverized coal circuit. A low selector is set in the oxygen circuit to compare the measured amount of pulverized coal with the amount of pulverized coal given by the load, and the lower one is taken as the given value of the oxygen circuit. When the load value is raised, the pulverized coal flow rate is greater than the given load value, which is selected by the high separator, and the oxygen flow rate increases accordingly by adjusting the oxygen-coal ratio. When the load is reduced, the pulverized coal flow rate is lower than the given value of the load, and is selected by the low selector, the oxygen flow rate is reduced first, and then the oxygen-coal ratio of the batching system is reduced.

(c) Description of the lock bucket logic system

Lock bucket PLC system mode includes operation, slag collection, slag discharge mode.

Related to lock bucket safety valve, lock bucket inlet valve, lock bucket outlet valve, lock bucket circulation pump inlet valve, chill chamber switch, chill chamber liquid level and other valves and field detection signals.

Methanol synthesis dosing strategy

Methanol synthesis part of the mixer is mainly based on simple ingredients, including the pressure after the first decompression of the loose gas, the pressure after the second decompression of the loose gas, the secondary production pressure of the steam pressure, the level of flash tank, the level of the methanol separator, the level of the alcohol washing tower, the outlet water of the boiler feed water preheater, the operating pressure of the drum, the heating gas pressure, etc.

Complex circuit batching mainly includes boiler level 3 impulse system.

The inner ring regulates the feed water flow in the boiler section, the outer ring regulates the drum level, and the feedforward is the secondary production medium pressure steam flow in the outlet section.

The safety interlock involved in the synthesis section is that when the drum level is low (less than the specified value), the interlock action stops the raw gas compressor and the synthetic gas compressor.

Closing remarks

The automatic batching system involves petrochemical, chemical, metallurgical, electric power, building materials, beer, paper and other industries, and has successfully implemented more than 4,000 engineering projects, including a large number of typical and characteristic projects. We look forward to working with more users in the coal-to-methanol industry to make progress together, so as to comprehensively improve the level of automatic dosing and economic benefits of the entire industry.