Intermittent Gas-making Plant Control Program
1.1 Gas-making Process Principle
Intermittent gas-making furnace is theequipment to convert coal to semi-water gas in most small and medium-sizedfertilizer plants and gas companies, and it is the first process to produce feedgas. The efficiency of gas-making furnace is directly related to the consumptionof feed coal and steam as well as gas production rate. Therefore, theconsumption of feed coal and steam of gas-making furnace accounts for more than70% in fertilizer plant.
The principle of gas-making furnace is to makethe coal burning, spray the burning coal with water vapor, enable watermolecules to react with burning coal to generate hydrogen and carbon monoxide,and the molecular formula is as follows:
C (burning) + H2O (steam) → CO ↑ + H2 ↑
Then oxygen is removed through burning furnace,and impurities are washed by gas washing tower to become feed gas required bythe next section and transported to gas cabinet for storage. In fertilizerindustry, nitrogen needs to be added during production for synthesis system tosynthesize nitrogen.
1.2 Gs-making Process Flow
The key equipment for intermittent gas-makingis gas-making furnace, which is generally divided into four specifications of ￠ 2.3m, ￠ 2.6m, ￠ 3.3m and ￠ 3.6m bysize, and divided into automatic coke adding and manualcoke adding by way to add coal. Automatic coke adding means that the operationautomatically adds coal at certain times, and a small amount of coal is addedat each cycle; manual coke adding means that a lot of coal is added manually ata time after several cycles; generally, ￠ 2.3mand ￠ 2.6m are manual coke adding furnace,while ￠ 3.3m and ￠ 3.6mare automatic coke adding furnace. The main equipments for intermittentgas-making include blower, gas-making furnace, up duster, down duster, wasteheat boiler, burning furnace (with automatic coke adding), gas washing tower,chimneys and steam drum, and the functions of these devices are as follows:
Blower provides blowing gas for gas-makingfurnace to make the coal in burning state.
Gas-making furnace produces coal-gas keyequipments with coal and steam,
Coal gas of up duster gas-making furnace isused for dust removal when going from bottom to top.
Coal gas of down duster gas-making furnace isused for dust removal when going from top to bottom.
Waste heat boiler is to cool coal gas andgenerate steam, burning furnace (automatic coke adding) is used for removingthe excess oxygen in coal gas, and gas washing tower is used for wash theimpurities in coal gas.
Chimney blowing gas discharges flue gas whennot being recovered, and it is emptied outside to prevent gas explosions.
Because the temperature of gas-making furnaceis very high, in order to protect furnace wall, a water jacket is installedoutside the furnace chamber, and steam drum is responsible for providing jacketwith water supply and storing the steam generated by jacket.
II. KeyControl Scheme:
2.1 Specific Description of Function KeysControl
1. Automaticfunction: the system moves in cycles according to the pre-set program ofblowing, up blowing, down blowing, secondary up blowing and blowing off.
2. Manual function: single-valve manual operation can be carried out atthis time, but explosion-proof safety chain rules should be followed.
3. Parking function: it is at safe parking state at this time, that is,only the chimney valve is opened, and other valves are all closed.
4. Parking lock: a lock is added when parking, which is used for preventfrom opening the furnace by mistake in repair.
5. Pause function: the process requires the 14 valves to maintain thecurrent status when pressing pause key, for example, when pressing pause key atthe second stage, that is, 20th second in up blowing section,the entire equipment should maintain the state at 20th second in upblowing section, until the pause key is cancelled, the entireequipment will begin to continue the original operation from the state at 20thsecond in up blowing section. It is used for blowing of manyfurnaces.
6. Step function: press step program to go into the next stage at the currentstage. It is also used for blowing of many furnaces.
7. Inertgas-making function: it is used when requiring inert gas.
8. Nitrogenadding function: it is used when adjusting H2/N2 ratio
9. Full-blowing up function: down blowing is changed to up blowing at thistime.
10. Blowing recovery function: it is generallyused in the process of recycling of blowing gas.
Flexible times at five stages and adjustablecontrol to switch time of the valve
The foremost characteristic of the technologyis flexibility to modify time at all stages. It is a key in the production toreduce consumption of coal and steam to adjust the cycle time according tocondition of the gas furnace and quality of coal, namely times of all stagesand switch times of all valves. Meanwhile, we must abide by the rule that totaltime of the five stages equals to the cycle time and the switch time of eachvalve does not exceed time of the very stage.
Build the five timer shafts of a cycle by fivefives stages and control time of every stage by five timers; timing constantsof the five timers are entitled via related calculation of the numerical valueand technology and type conversion, then all stages can be adjusted accordingto technological condition. If the upgoing temperature is on the high side, thedown-blowing time should be extended; if the downgoing temperature is on thehigh side, then the up-blowing time should be extended; the air time can beadjusted according to condition of coal and furnace. A symbol switch is outputfrom times of five stages, from which the switch time of each single valve canbe calculated. Thus, change of times of all stages will cause automatic changeof every valve, which will carry out new production proposal without timeconflict.
Be at safe state consistently while switching.
When switchover from automatic and parkingstate to manual operation, all valves are close firstly, then they are openedand closed via the manual control key; after switchover form manual operationto automatic operation, all manual control keys must be closed to ensure safeswitchover.
Be at safe state while parking and driving atany time.
When it is requested to park at thedown-blowing stage, drive is forbidden at the blowing stage and blowing-off stage;drive is forbidden at the down-blowing stage when parking is at the blowing andblowing-off stage. If the above situations happen, the complete up-blowingfunction should be carried out for 30seconds firstly, then the system turns tonormal operation automatically; if not, it operates normally.
There are many other processes from parking todriving, thus, the system must has memory function at the parking stage and judgmentfunction at the driving stage. Besides, it must have the function to removeparking memory after normal driving so as to make preparation for next time.
Concrete operation takes on as follows: theparking sign is recorded in the locked coil under down-blowing, blowing-off orblowing state when the parking or automatic state is removed, which is keptwith the stage sign of next driving to judge normal driving, if it is abnormal,30 second complete up-blowing function is triggered, then the paring memorysign is unlocked after the complete up-blowing; if it is normal, the parkingmemory sign is directly unlocked.
Only this cycle is requested to take effectafter partial function keys are pressed down, the below cycle recoversautomatically, and the function key rebounds automatically.
Press down the drive of the function key tolock executive command of the coil, then drive two unlocking coils, one is usedto unlock coil of the function key, the other is used to rebound the button andreturn to the original color.
Display function of integral image.
There is setting time, current time and currentstate of each furnace on the picture at five stages, meanwhile, horizontaldynamic light cross is used to vividly display current time, state of eachvalve is also indicated by striking red light, and information of the furnacewill be clear at a glance. Other routine analog quantity such as steam pocket liquidlevel and pressure etc can be controlled conveniently. Up-blowing anddown-blowing coal gas temperature and the temperature curve flowing in thefurnace can be recorded and checked for analyzing condition of the furnace.
Ⅲ optimalcontrol scheme
Ahead steam— optimal control scheme viasteady pressure:
In adjustment of steam, routine steam steadypressure method is not suitable for requirements due to particularity of gasmaking by steam, there exists serious hysteresis phenomena; thus, we useroutine steady pressure and feedforward method, namely you should turn up thesteam control valve in direct ratio and increase steam quantity in advancebased on common steady pressure adjustment and according to total number ofteam valves while blowing steam instead of turning up the steam adjusting valveafter the steam pressure falls; furthermore, you should adjust closing by feedforwardwithout blowing steam, only steam steady-pressure adjustment takes effect, becausetemperature in the furnace changes from high to low in blowing steam, thus, differentialcan be used in blowing steam to reach small to large so as to promote the resolutionratio of steam. The differential constant and time can be adjusted according toworking condition on the scene.
Automaticoptimizing control scheme at blowing time, up-blowing time and down-blowingtime:
According to the upgoing coal gas and thedowngoing coal temperature at last stage, the up-blowing and down-blowing timeat next stage can be confirmed by the optimization method in consideration oftemperature change between cycles; in order to keep stable production, you canadjust based on the manual setting time appropriately.
Optimal control scheme with alternative hydrogen-nitrogenratio
Introduce data of recycle hydrogen andconversion hydrogen into the system and adjust controllable hydrogen-nitrogenratio at the nitrogen adding time. Due to serious hysteresis in controlling hydrogen-nitrogenratio, gray prediction and fuzzy control should be conducted according totechnological condition.
Automatic blowing queue optimal control
Automatic blowing queue, for example, 9furnaces are a steam main, which allows 2-3 furnaces blowing together; as fortwo steam mains, there can be 1#～5#queue, 6#～9#queue, and 1#～3#queue, 4#～6#queue, 7#～9# queue.