CN102039059A

CN102039059A - Method for controlling top of fine propylene tower

Info

Publication number: CN102039059A
Application number: CN2009101534804A
Authority: CN
Inventors: 邱向阳
Original assignee: China Petroleum and Chemical Corp
Current assignee: China Petroleum and Chemical Corp
Priority date: 2009-10-10
Filing date: 2009-10-10
Publication date: 2011-05-04
Anticipated expiration: 2029-10-10
Also published as: CN102039059B

Abstract

Disclosed is a method for controlling the top of a fine propylene tower. The liquid level gauge of a backflow tank (LC4108) on the top of the fine propylene tower is in series connection with a control valve (FC4119) for controlling backflow; a detection and control unit (AC4101) for measuring the purity of propylene is in series connection with a control valve (FC4120) for controlling the outward tossing amount of propylene; and a detection and control unit (PC4C103) for controlling pressure on the top of the tower is connected respectively with each control valve on cold and heat bypass. The invention is characterized in that the pressure of a tower top is controlled and deemed as a major parameter, the backflow of the tower top is controlled and deemed as a secondary parameter, and both the pressure and the backflow of the tower top employ PI control means. The invention enables high yield of propylene, which promises richer economic benefit for a company. Moreover, the invention contributes to more stable operation and lower labor intensity of operators.

Description

A kind of control method of fine propylene cat head

Technical field

The present invention relates to a kind of control method of fine propylene cat head.

Background technology

Thought always in the past that the stable control of pressure was the main points of rectifying column operation, so, adopting fixedly reflux ratio in the past, pressure is thrown control automatically.Opening greatly greatly of thermal bypass closed, though can be controlled at pressure on the value, but cause the fluctuation of vibration up and down of return tank liquid level, the also corresponding fluctuation that causes fine propylene purity simultaneously, when purity was very low, the propylene amount of getting rid of outward closed very for a short time, when purity is very high, the propylene amount of getting rid of is outward opened very greatly again, sometimes in order to keep the return tank liquid level, significantly turns down the propylene amount of getting rid of outward.This itself is exactly unsettled phenomenon, is in the stage of passive adjusting fully, and the propylene high yield is difficult to realize.So when liquid level changed, we attempted adopting the way of regulating hot water amount at the bottom of the tower, but effect is bad, and are very blunt, and a kind of sensation that Distant water cannot quench present thirst is arranged.And when the decline of return tank liquid level is very fast, carries the hot water amount and cause the pressure drop of whole tower to increase, finally cause liquid flooding.Progressive to some extent finally, when expecting the return tank liquid level and will rising suddenly and sharply or slump, at once with thermal bypass manual adjustments liquid level, replenish adjusting with capacity of returns again, this is in fact still in a rush, be difficult to accomplish accurate adjusting, and pressure can change all at any time, what change be difficult to hold, it is also very big to stare at table intensity.The operation technique of each class is ununified in addition, and each have their own method, product yield and quality are all unstable.

Fig. 1 is seen in the connection of fine propylene cat head, and its existing problems are: 1, and oepration at full load, operating condition is relatively harsher.2, this column foot originally is full manual operation, and some important operation control parameters (as: purified propylene AC4101 and propylene discharging FC4120, return tank liquid level LC4108 and capacity of returns FC4119) all can't be thrown automatic control.3, each class operation thinking difference causes the operating mode of tower extremely unstable.This tower volume is big, in case settle out need be for a long time in fluctuation.These factors all influence the output of fine propylene.If can be connected in series automatic control to five important parameters of cat head respectively, operation will be stablized manyly certainly.But, exist two problems can not solve here always, cause these control loops all not throw serial connection.First: should can not determine as major loop or principal parameter with which on earth.Second: how pid parameter should be set at the best.These two problems are perplexing us always.

Purified propylene on each layer of fine propylene cat head tower tray is all different, be the staged downward trend, when pressure oscillation, when the return tank liquid level rises, when distillating line than the low-purity propylene component by cat head in a large number, the AIC4101 chromatogram has reflected this point immediately, though V4004 is not necessarily at once defective, will worsen at once.So when other parameter stability, the rising of liquid level and decline have directly reflected the increase and the minimizing of overhead, purity descends if liquid level rises then, and purity rises if liquid level descends then.If a stable liquid level can be arranged, then purity also is stable, and the variation of purity is just very little, can obtain stable operating mode by trickle adjusting, thereby realizes the propylene high yield.So the control liquid level is from the transformation of original passive adjusting to active adjustment.

Summary of the invention

Technical problem to be solved by this invention provides a kind of control method of fine propylene cat head, and it can have more the economic benefit that fine propylene can improve company, and this invention has simultaneously improved the smooth operation rate greatly, has alleviated operating personnel's manipulation strength.

The present invention solves the problems of the technologies described above the technical scheme that is adopted: a kind of control method of fine propylene cat head, and the return tank liquid level gauge (LC4108) of its fine propylene cat head is connected in series with the control valve (FC4119) of capacity of returns control; The detection control module (AC4101) of measuring purified propylene with control propylene outward the control valve of the amount of getting rid of (FC4120) be connected in series; The detection control module (PC4C103) of control tower top pressure is connected in series respectively with each the road control valve in the cold and hot bypass, it is characterized in that: the pressure of return tank liquid level and cat head adopts PI control.

As improvement, purified propylene also adopts PI control.

Its PI control parameter of the pressure of cat head P value 7-13% is gain; I value 〉=700min.

Its PI control parameter of return tank liquid level P value 1.3-1.7% is gain; I value 15-20min.

Its PI control parameter of purified propylene P value 2.7-3.3% is gain; I value 85-115min, detecting the control module range is 0-1%, represents the purified propylene of 99-100%.

Control valve (FC4119 and FC4120) is flow-control, belongs to the anhysteretic parameter, as long as regulate sensitivity, the parameter setting is respectively (P value 0.4%; I value 0.5min) and (P value 0.6%; I value 0.5min).

Compared with prior art, the invention has the advantages that: can be applied on the same apparatus, as the fine propylene tower, China Petrochemical Industry, PetroChina Company Limited., the such device of CNOOC have a lot; Secondly can be applied on the similar similar installation; The theory of PI parameter almost can be used in the operationlocation of any hysteresis, it can obtain the effect of the leading adjusting of differential D under I long enough time of integration condition, it can significantly improve product yield and quality, improve the steady rate of device, reduce operating personnel's manipulation strength.

Description of drawings

Fig. 1 is the control principle figure of fine propylene cat head;

The specific embodiment

Below in conjunction with accompanying drawing the present invention is described in further detail.

Following the Several Parameters of fine propylene tower so that the liquid level influence degree is arranged from high to low: thermic load, the propylene amount of getting rid of, inlet amount and composition outward at the bottom of pressure, overhead reflux amount, the tower.In the actual production, the hot water temperature is still more stable, and the stable of hot water is advantageous advantage at the bottom of the tower, generally do not do adjusting, closes bond energy and guarantees that higher reflux ratio is just passable.And the propylene amount of getting rid of, inlet amount and the variation formed liquid level outward is gradual, and a spot of adjusting is little to the influence of return tank liquid level.Pressure, overhead reflux amount have just become the key of control return tank liquid level.These two parameters have the greatest impact to liquid level, and particularly the variation of pressure can cause the sudden change of return tank liquid level.So it is best, the sensitiveest to control liquid level with pressure and capacity of returns.

How to come controlled pressure so? it is necessary automatically that pressure is thrown, and manual adjustments is unsuccessful certainly.

Throw the selection that automatic key is the PI parameter.Here will hold two principles.1: the switch amplitude of thermal bypass can not be very greatly when pressure changed, though the very big variation that can offset a part of liquid level of amplitude, easily frequent edge is not regulated leeway more, and the result is that outer behaviour's start-stop air cooling and interior behaviour regulate air cooling fan blade angles increased frequency.Be that the easy Kai Detai of thermal bypass is big on the one hand in addition, cause the instability of liquid level.2: when pressure changed, thermal bypass just changed.Though pressure and set-point have deviation can not do adjusting again, as long as pressure (is reference with the technic index) in allowed band just can.So must grow the time of integration.Because if pressure descends, deviation exists, though this moment, pressure no longer changed, thermal bypass meeting one under integral action is headed straight for big, and thermal bypass is opened the big liquid level that influences, and liquid level is descended.At this moment if to keep liquid level constant, need reduce capacity of returns.But the lasting decline of capacity of returns just causes reflux ratio not enough at once.Influence the separating effect of column plate, cause purified propylene to descend.If instead thermal bypass constantly turns down, capacity of returns continues to increase and causes liquid flooding easily.

In order to satisfy principle one, gain P value should be selected a little bit smaller, and is optimum through calculating 5～10%.In order to satisfy principle two, should be being placed on the most blunt position the time of integration, we select 1000min (the DCS maximum is 1440min).Both its PI control parameter of the pressure of cat head P value 10%; I value 1000min, the regulating effect of thermal bypass is so like this: when pressure changed, thermal bypass just changed, and had offset the liquid level variation that a part causes because of pressure changes, and remaining liquid level deviation is regulated by capacity of returns; When pressure was constant, even depart from set-point, thermal bypass was not done adjusting yet.When pressure during, just regulate the air cooling load near the bound of technic index.

The control valve FC4119 serial connection of the return tank liquid level gauge LC4108 of the T4003 of fine propylene tower and control capacity of returns, holding a principle, is exactly liquid level when deviation occurring, and capacity of returns can in time be regulated rapidly, make the return tank liquid level return to set-point rapidly, such third rare purity changes just minimum.So the return tank liquid level gauge LC4108 degree of regulation of the T4003 of fine propylene tower is had relatively high expectations, we have selected the relatively short time of integration.

Be summarized as follows: return tank liquid level gauge LC4108, it is Center Parameter, T4003 return tank liquid level gauge and capacity of returns tandem are equivalent to the major loop of these three tandems, this parameter request is regulated rapidly, but require capacity of returns not fluctuate back and forth, it is proper to control its parameter P:1.5%, I:18min through the return tank liquid level PI of long-term test, the basic ripple disable of liquid level (in ± 0.3%), when changing, condition such as heat-obtaining, inlet amount at the bottom of the tower can rapidly, accurately adjust capacity of returns, full tower stable operation guarantees that purified propylene can not rise and fall sharply and quickly.

The detection control module PC4103 of tower top pressure, this parameter request is basicly stable, less demanding to deviation, but can not frequently regulating back and forth, cold and hot bypass influences return tank V4004 liquid level, it is proper that the PI of tower top pressure controls its parameter P:10%, I:1000min after tested, can guarantee more greatly that in the morning and evening temperature Change pressure basicly stable (deviation is arranged) can reduce the influence to return tank V4004 again.

The detection control module AC4101 of purified propylene, require to regulate slower, responsive to variation tendency, deviation is not too responsive, can not significantly change, it is proper that the PI of purified propylene controls its parameter P:3.0%, I:100min after tested, effectively influences the return tank liquid level by the fine setting to the propylene discharging, it is more steady to have reached operation, the purpose that the purified propylene fluctuation diminishes.

Subtabulation in other serial connection control as the control valve FC4119 of control capacity of returns, control fine propylene outward the control valve FC4120 etc. of the amount of getting rid of only require and can in time move just that pid parameter is less demanding because with the master meter action.

Facts have proved through our company, this method can realize energy-conservation when underload, the maximization of gratifying realization propone output when high load capacity, the ratio of actual propone output/theoretical propone output is brought up to about 0.865 by 0.845, the average daily output of propylene has increased about 10 tons, in 3000 yuans of the price differences after propylene and the liquefied gas deduction operating cost, can increase by 1,050 ten thousand yuans of benefits every year.

Claims

1. the control method of a fine propylene cat head, the return tank liquid level gauge (LC4108) of its fine propylene cat head is connected in series with the control valve (FC4119) of capacity of returns control; The detection control module (AC4101) of measuring purified propylene with control propylene outward the control valve of the amount of getting rid of (FC4120) be connected in series; The detection control module (PC4C103) of control tower top pressure is connected in series respectively with each the road control valve in the cold and hot bypass, it is characterized in that: the pressure of return tank liquid level and cat head adopts PI control.

2. the control method of fine propylene cat head according to claim 1 is characterized in that: purified propylene also adopts PI control.

3. the control method of fine propylene cat head according to claim 1 and 2 is characterized in that: its PI control parameter of the pressure of cat head P value 7-13% is gain; I value 〉=700min.

4. the control method of fine propylene cat head according to claim 1 and 2 is characterized in that: its PI control parameter of return tank liquid level P value 1.3-1.7% is gain; I value 15-20min.

5. the control method of fine propylene cat head according to claim 1 and 2 is characterized in that: its PI control parameter of purified propylene P value 2.7-3.3% is gain; I value 85-115min, detecting the control module range is 0-1%, represents the purified propylene of 99-100%.