air pressure control muz done

8/17/2019 Air Pressure Control Muz Done

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[AIR PRESSURE CONTROL]

TABLE OF CONTENTS

1.0 OBJECTIVES 21.0SUMMARY 3

2.0INTRODUCTION AND THEORY 43.0RESULTS AND DISCUSSIONS 7

5.0 CONCLUSION & RECOMMENDATION

6.0 REFERENCES 21

APPENDI 2

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1.0 OBJECTIVES

The objectives of this experiment Air Pressure Process Control are:

i. To identify the important components of the air pressure control system and to

mark them in the P&I ia!ram.ii. To carry out the start"up procedures systematically.iii. To control the pressure in sin!le capacity and t#o capacity processes usin!

PI Controller.

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2.0 SUMMARY

This experiment #as basically conducted in order to identify all of the important

components of the air pressure control system #hile carry out the start"up

procedures systematically and implement the control of pressure throu!hout in the

sin!le and t#o capacity processes usin! PI controller. In this experiment$ air

pressure process control model AP% is used. The AP% uses air to stimulate a

!as phase pressure process. 'ased on the results$ it can be seen that the

differences bet#een sin!le and t#o capacity process in term of response are not

much differ. (o#ever$ there are some variables that has been manipulated in order

to examined the retention time$ overshoot and also the settlin! time of the !raph to

reach its steady state. The P')$ TI) and also T) #as set to various value #hich

then sho#in! a different response to#ards the disturbance. The proportional band

*P'+ is a type of closed"loop feedback control in #hich a constant value is multiplied

#ith the error in order to adjust the output. The sin!le capacity is more !ood

compared to t#o capacity because more efficient and consume time. *,ummary of

-esult+

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3.0 INTRODUCTION

The study of material behaviour under pressure is to investi!ate the #ide

variety of discipline of air pressure control. Pressure vessels play important role in

chemical industries as stora!e vessels for !as phase components$ reaction vessels

to carry out a !as phase reaction. Precise control of pressure in the pressure vessels

is necessary in order to maintain a constant concentration of components in the

vessel. 'esides to maintain the number of moles in the vessel$ the pressure control

itself help to protect the vessel from bein! dama!ed due to very hi!h pressures

*'ennett$ )%%+. The arran!ement uses the controlled release of air already in

stora!e to stabili/e the air pressure delivered into the main pipin! header leavin! the

compressor room. Pressure at control valve outlet is sensed and air flo# is

continuously adjusted to correct the deviations from set point. It #orks on the

principle that #hen compressed air expands$ the pressure decreases and$

conversely$ #hen air compresses$ the pressure increases. Therefore$ if more air is

flo#in! a#ay from the balance point than in$ the pressure !oes do#n and the control

valve modulates open to release more air from stora!e to brin! it back to the set

point. The opposite action occurs if more air is flo#in! into the balance point than

a#ay as the valve modulates closed to hold air back in stora!e. 0i!ure ).1 is a

schematic illustration of 2eneral arran!ement of an electropneumatic pressure

reducin! station:

F!"#$% 1.0 2eneral arran!ement of an electropneumatic pressure reducin! station

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The benefit from applyin! air pressure control is that the plant air pressure

can be maintained the lo#est optimum level needed to reliably sustain production.

Pressure Control also prevents the plant air pressure from risin! as leaks are

repaired and air #aste is reduced. If nothin! is done to control the pressure$ it can

creep up and cause more air to vent out of other escape points in the system such

as condensate drains$ open air blo#in! devices$ unrepaired leaks$ and unre!ulated

points of use. There are also operational savin!s from reducin! leak demand and

optimi/in! air use. Air flo# across filters and dryers #ill be less. Pressure drops in

the pipin! distribution system #ill decrease. 3aintenance costs #ill !o do#n. Air

pressure control is an excellent tool to use for controllin! air leaka!es of all types.

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4.0 DISCUSSION

This experiment has been desi!ned to achieve three main objectives$ namely to

identify the important components of the air pressure control system and to mark them in theP&I Diagram, to carry out the start-up procedures systematically and lastly to control the

pressure in single capacity and two capacity processes using PID Controller.

The first obecti!e has a !ery significant link with the successful of the e"periment, in which

if the important components of the air pressure control system to be identified has not been

done, the students cant conduct the e"periment successfully. This has been done, and has

been attached with marked the important components of the air pressure control system on

the P&I Diagram. #e"t, is to carry out the start-up procedures systematically. This obecti!e

will only indicate if it was successfully conducted or not, when the e"periment gi!e goodresults. $ince start-up procecedures cant be done wrongly, as it will gi!e negati!e results

during the achie!ement of the third obecti!e. The third obecti!e was to control the pressure

in single capacity and two capacity processes using PID Controller. This e"periment has to

type of capacity namely, single capacity with only the usage of single tank, T% to operate the

control system with following route'

Single capacity process: AR91-MV91-T91-PLI-B92-FI92-PCV91-VP

(hile the second one is double capacity, which will utili)e both tanks, T% and T%* to

control the air pressure system with following route'

To-capacity process AR91-MV91-T91-PLI-MVI-T92-MV92-FI92-PCV91-VP

+oth will be used with PID control system to compare and contrast the type of response gi!en

by the system.

or PID Control Of Pressure In Single Capacity Process in T91 (3.3 in Lab Manual),

only !essel T% is used where as essel T%* is by-passed. The set point of the air pressure for

this process at PIC% as SV = 15 psig. Then, the PID controller was set with the f irst (I) trial

values: PB1 = 70%, T11 = 40 s, TD1 = 0 s. The response can be seen in the graph asindicated at 3.3(9) in the graph. Then, the MV is decreased about 10%. The response has

been observed and marked on the graph paper as 3.3 (10). As to compare both peak, its

observed that, at initial (before the MV has been reduced about 10%), the peak has higher

amplitude, compared to the peak that has been reduced the MV about 10%, that could

achieve the SV of 15psig faster than the initial value.

Then, the controller was set the PID with the second (II) trial values: PB1= 45%, TI1 = 30

s, TD1 = 0 s. This values shows the PB or proportional band with reduced to 45% and the

Integral time has been reduced to 30s. Then, the MV values have been reduced of 10%. The

peak has been marked on the graph paper with 3.3 (12). If compared this PID (II) with PID

(1), the peak almost the same, but with a more steeper peak that causes the process to achieve

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the set point faster.

Next, third (III) trial values for the PID controller'PB1 = 20%, TI1 = 10 s, TD1 = 2 s has

been introduced to the controller. Important: This control values has derivative values with 2s

that the previous controller ( PID 1 and PID 2) don’t have. Then, the MV has been decreased

by 10%. The peak has been marked as 3.3 (15) on the graph paper. This peak shows a veryshort oscillatory and small peak and the more fast response to achieve set point. Due to the

small value of proportional values ( the smallest among the 3 PID control settings above), and

also give the Integral time that is suitable with 10s, and with derivative control has been

added with 2s, give a very fast response to the control system.

Figure 1: Comparison of P, PI and PID controller response.

As shown in Figure 1, with the presence of derivative (D), the PID controller response

with faster, less oscillatory and without offset. Thus, theoretically, its aligned and merge with

the results obtained from the experiment. As to compare the three PID values, it can be

discussed that higher the PB value – higher the amplitude and oscillatory peak will be

produced as can be seen in the PID 1 above. When reduced the PB value, the peak is hassmaller amplitude likewise in PID 2. Then, when derivative and smaller PB value has been

introduced, the best response with faster settling time has been achieved in PID 3.

Then, the PID Control Of Pressure In Two Capacity Process (T91 & T92) has been done (3.4

in Lab Manual). In this experiment, two capacity or both tank will be utilized to control the

air pressure system. The control valve has been opened (PC%/ about 012 from PIC% by

adusting with 3 4 012. The set point has been set, of the air pressure for this process

PIC% as $V = 18 psig. The PID controller has been set with the f irst (I) trial values: PB1 =

70%, T11 = 40 s, TD1 = 0 s. As its been marked on the graph paper with 3.4(9), it shows a

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large amplitude, sluggish and longer response time. Then, the MV has been brought to 40%.

The response has been marked with 3.4(11). The response shows increasingly faster tuning

(as shown response in Figure 2) that it has a steep peak with faster settling time to achieve set

point. The response is oscillatory but achieve SV faster than the MV with 50%.

Figure 2: Increasing faster tuning with steep peak achieved

Then, second (II) trial values: PB1= 45%, TI1 = 30 s, TD1 = 0 s has been

introduced. The response has been marked with 3.4(13) and its hows an oscillatory response.

Then the MV has been decreased by 10% and the responsed has been marked on the graph

paper with 3.4 (14). This response is a smaller amplitude, less oscillatory and faster response

time compared to the first PID value. This is even both tank has been operated, but still, the

PB value reduced, it still obey the theory of: higher the PB value – higher the amplitude and

oscillatory peak will be produced.

Lastly, the third (III) trial values for the PID controller'PB1 = 20%, TI1 = 10 s, TD1

= 2 s has been set. The response has been marked with 3.4 (16) and it shows a more lesser

oscillatory and faster settling time compared to ALL PID values set in this experiment

previously. It achives the SP with straight line without sluggish response. Then, disturbance

has been introduced, by dropping the MV value by 10%, again, a lower amplitude, faster

reponse and non-oscillatory response has been achieve, and it’s profoundly could be stated

that this PID values is the best among all the PID values suggested in this experiment as

stated reasons above.

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5.0 CONCLUSION & RECOMMENDATIONS

higher the PB value – higher the amplitude and oscillatory peak will be produced.

To improve this experiment in the future$ some recommendation had been

proposed for example before startin! the experiment$ it is advisable to recheck the

entire valve and pipelines so that it4s condition follo#ed the procedure correctly. It is

advised to increase the value of P' for each trial and decrease the value of TI) in

each experiment so that the dampin! oscillation for each trials and response time #ill

decreases to reach set point and steady state respectively. 'esides$ students that

handle the machine should !et the overvie# ho# the machine runnin! and also

should have some basic kno#led!e to obtain a correct readin!. 3ainly$ the chart

paper should be placed correctly in order to avoid error durin! the recordin!.

0urthermore$ durin! the chan!es of set point and other related parameters the

student should jot do#n for discussion purpose and their understandin!

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6.0 REFERENCES

• 'ennett. ,.$ *)%+. A history of control en!ineerin! *5th ed.+. ,tevena!e$

(erts.$ 6.7.: P. Pere!rinus on behalf of the Institution of 8lectrical 8n!ineers$9ondon$ c)%%$ )1");.

• Cou!hano#r$ .-.$ *)%%)+. Process ,ystems Analysis and Control$ nd 8d.$

3c2ra# (ill$ ". *)%%%+. ,ome Conventional Pocess Control ,chemes$ Department

of Chemical and Process Engineering University of Newcastle$ ".

• ,vrcek$ >. ?.$ onald$ 3.$ ?oun!$ '. -. *8ds.+. *)%%5+. A Real-Time Approach

to Process Control, ol!tions "an!al . >iley. 1"55.

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air pressure control muz done

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