Expert System Applications in Chemistry - American Chemical Society

Chapter 14

Optimizing Combustion in Multiple-Burner Installations Terence C. Fogarty, D. Paul Jenkins, and Jon Mortimer

Downloaded by CORNELL UNIV on October 11, 2016 | http://pubs.acs.org Publication Date: September 1, 1989 | doi: 10.1021/bk-1989-0408.ch014

Bristol Transputer Centre, CSM Department, Bristol Polytechnic, Coldharbour Lane, Bristol BS16 1QY, United Kingdom

Rules for adjusting the air inlet valves to each of a number of burners with a common flue, depending on the concentrations of oxygen and carbon monoxide monitored in that flue, were elicited from experts. The rules have been embodied in an expert system, written in PROLOG, which is used to optimise combustion in multiple burner installations. The system was tested on PROLOG simulations of multiple burner installations, each burner being modelled by a number of perfect burners. It was then run on a twelve burner zone of a 108 burner furnace on a continuous annaeling line for rolled steel. A system which learns i t s own rules by modifying the expert rules in the light of experience is being developed and will be tested against the expert system on a multiple burner boiler plant.

The Problem. The problem is to automatically and continually optimise combustion in a multiple burner furnace or boiler plant by altering the air inlet valve to each of the burners depending upon the carbon monoxide and oxygen readings taken from their common flue. The optimum air/fuel mixture w i l l be different for each burner, because of their varying type, age and condition, and i t can be achieved for a given supply of fuel by individually adjusting the air inlet valve to that burner. A typical multiple burner furnace has over one hundred small burners arranged in zones of one or two dozen burners with two exhaust stacks per zone each taking the waste gases of half the burners of that zone. A typical multiple burner boiler plant has six double burner boilers exhausting via three shared stacks. At present, the air/fuel ratio of each burner in a multiple burner installation in the steel industry w i l l be manually adjusted about every 3 to 9 months by a fuel technician using portable analysers to measure the carbon monoxide and oxygen concentrations in the waste gases of each burner. 0097-6156/89/0408-0180$06.00/0 o 1989 American Chemical Society

Hohne and Pierce; Expert System Applications in Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


14.

FOGARTYETAL.

Optimizing Combustion in Multiple-Burner Installations 181

R e l a t e d Work. As t h e c o s t o f a n a l y s e r s has come down, many s i n g l e burner b o i l e r s have had a i r / f u e l r a t i o s e t p o i n t c o n t r o l l e r s added w i t h a feedback l o o p from e i t h e r an oxygen (1_) o r a carbon monoxide (2) a n a l y s e r . P r e s s e r and S e m e r j i a n ( 3 ) g i v e a good r e v i e w o f t h i s work up t o t h e mid 1980's. The optimum oxygen s e t p o i n t v a r i e s depending upon t h e k i n d o f b u r n e r , f i r i n g l e v e l , l o a d , t y p e o f f u e l , t e m p e r a t u r e , h u m i d i t y , amount o f tramp a i r and t h e d e t e r i o r a t i o n i n the burner. The carbon monoxide r e a d i n g i s v e r y v o l a t i l e a t near optimum l e v e l s . A c o m b i n a t i o n o f t h e two r e a d i n g s i s thought by most e x p e r t s t o be t h e b e s t approach ( 4 - 7 ) . A r u l e based approach t o p r o c e s s c o n t r o l has f o r many y e a r s p r o v i d e d an a l t e r n a t i v e t o t r a d i t i o n a l methods i n t h e form o f f u z z y l o g i c c o n t r o l ( 8 , 9 ) . S i n c e t h e advent o f e x p e r t systems, r u l e b a s e s have been used f o r f a u l t d i a g n o s i s [ 1 0 ] , t o a d v i s e o p e r a t o r s (11.), t o a i d c o n t r o l e n g i n e e r s when i n s t a l l i n g PID c o n t r o l l e r s ( 1 2 ) , t o p r o v i d e e x p e r t o n - l i n e t u n i n g f o r PID c o n t r o l l e r s ( 1 3 ) , and t o c o n t r o l p r o c e s s e s w i t h o u t t h e u s e o f f u z z y l o g i c (14,15). The

Rule-Base

The O r i g i n o f t h e R u l e s . R u l e s f o r a d j u s t i n g t h e a i r i n l e t v a l v e s t o each o f a number o f b u r n e r s w i t h a common f l u e , i n w h i c h t h e c o n c e n t r a t i o n s o f oxygen and carbon monoxide a r e m o n i t o r e d , were e l i c i t e d from energy e n g i n e e r s ( 1 6 ) and coded i n t o PROLOG. The r e s u l t i n g r u l e b a s e embodies t h e p r a c t i c e o f t h e f u e l t e c h n i c i a n who p e r i o d i c a l l y tunes m u l t i p l e burner i n s t a l l a t i o n s t o g e t h e r w i t h t h e e x p e r t i s e o f t h e energy e n g i n e e r who has d e v i s e d a system f o r t h e c o n t i n u o u s o p t i m i s a t i o n o f such i n s t a l l a t i o n s . The Type o f R u l e . The r u l e s a r e b a s i c a l l y o f t h e s i t u a t i o n - a c t i o n t y p e , where t h e s i t u a t i o n i s governed by carbon monoxide and oxygen r e a d i n g s , c l a s s i f i e d a c c o r d i n g t o c o n s t a n t o r v a r i a b l e system parameters, and t h e a c t i o n i s a c o m b i n a t i o n o f adjustments t o a i r i n l e t v a l v e s e t t i n g s and system parameters. A l l t h e r u l e s a r e o f t h e form: " I F s i t u a t i o n THEN a c t i o n b u t c h a i n s o f up t o t h r e e o f t h e s e a r e accomodated t o e n c a p s u l a t e t h e procedures o u t l i n e d by t h e e x p e r t s . The l o n g e s t c h a i n s a r e t h e r e f o r e of t h e form: 1 1

" I F s i t u a t i o n 1 THEN a c t i o n 1 THEN I F s i t u a t i o n 2 THEN a c t i o n 2 THEN I F s i t u a t i o n 3 THEN a c t i o n 3" w h i c h means t h a t t h e r u l e b a s e i s guaranteed t o r e a c t t o a c o m p l e t e l y changed s i t u a t i o n w i t h i n t h r e e i n t e r a c t i o n s w i t h t h e i n s t a l l a t i o n . T h i s goes some way towards s a t i s f y i n g t h e r e a l - t i m e c o n s t r a i n t s . A s s o c i a t e d w i t h each o f t h e r u l e s i s a r e p o r t c l a u s e w h i c h updates t h e o p e r a t o r s c o n s o l e and/or l o g s a message depending upon t h e s i t u a t i o n w h i c h caused t h e r u l e t o f i r e . C l a s s i f i c a t i o n o f S i t u a t i o n s . Three k i n d s o f s i t u a t i o n a r e c o v e r e d by t h e r u l e s . F i r s t , t h e r e a r e problem s i t u a t i o n s w h i c h r e q u i r e f a u l t d i a g n o s i s and p o s s i b l y s a f e t y measures. Second, t h e r e a r e


182

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s i t u a t i o n s i n w h i c h a l l t h e equipment i s assumed t o be w o r k i n g c o r r e c t l y b u t t h e a i r / f u e l r a t i o o f some o r a l l o f t h e b u r n e r s i s f a r from optimum. F a i r l y d e c i s i v e c o n t r o l measures a r e r e q u i r e d h e r e . T h i r d , t h e r e i s t h e most d e s i r a b l e s i t u a t i o n , i n w h i c h a l l o f t h e b u r n e r s a r e g i v i n g n e a r optimum p e r f o r m a n c e , r e q u i r i n g o n l y c h e c k i n g and f u r t h e r o p t i m i s a t i o n measures. Each o f t h e r e a d i n g s , oxygen and c a r b o n monoxide, i s c l a s s i f i e d as one o f : v e r y low, low, O.K., h i g h o r v e r y h i g h , a c c o r d i n g t o parameters w h i c h remain f i x e d e x c e p t f o r t h o s e d e l i n e a t i n g t h e optimum oxygen r e a d i n g . The change i n c a r b o n monoxide s i n c e t h e l a s t r e a d i n g i s c l a s s i f i e d as one o f : n e g ( a t i v e ) , n i l o r p o s ( i t i v e ) , n i l b e i n g p o s i t i v e b u t l e s s t h a n a c a l c u l a t e d amount. T h i s amount i s t h e d i f f e r e n c e between t h e l a s t r e a d i n g and t h e upper optimum l i m i t f o r c a r b o n monoxide d i v i d e d by t h e number o f b u r n e r s . control limits optimum limits

fault diagnostic and s a f e t y r u l e s 1 1 i i t i con t r o l r u l e s 1 1 I I optimi sation rules

very high

high

oxygen o.k.

1

1 1

^optimum j limits

control limits

low « 1 1

very low very low

high

1

I 1 1 o.k.

1

low

1 1 1 1

very high

c a r b o n monoxide class F i g u r e 1.

C l a s s i f i c a t i o n o f s i t u a t i o n s and c l a s s e s o f a c t i o n

The c l a s s i f i c a t i o n o f s i t u a t i o n s and c l a s s e s o f a c t i o n r e q u i r e d i s i l l u s t r a t e d i n F i g u r e 1. E v e r y e v e n t u a l i t y i s c o v e r e d by a r u l e and t h e r e a r e no c o n f l i c t i n g r u l e s f o r any s i t u a t i o n . I n PROLOG a r u l e t a k e s t h e form: action(02,C0,C0_change,Rule)

:- { l i s t o f a c t i o n s }


14. FOGARTYETAL.


where "02" i s i n s t a n t i a t e d t o t h e oxygen, "CO" t h e carbon monoxide and "C0__change" t h e change i n c a r b o n monoxide c l a s s i f i c a t i o n s , r e s p e c t i v e l y , and " R u l e " t o t h e number o f t h e r u l e i n t h e c h a i n . The maximum number o f r u l e s p o s s i b l e i n t h e system i s thus 5*5*3*3 = 225 w h i c h has a c o r r e s p o n d i n g maximum s e a r c h t i m e , thus a l s o h e l p i n g t o satisfy real-time constraints.


C o m p o s i t i o n o f A c t i o n s and Examples o f R u l e s . A l l t h e p r o c e d u r e s d e s c r i b e d by t h e e x p e r t s c a n be broken down i n t o f o u r t y p e s o f a c t i o n . There a r e a c t i o n s w h i c h a l t e r one o r a l l o f t h e v a l v e s e t t i n g s , a c t i o n s w h i c h a l t e r one o r a l l o f t h e increments by w h i c h t h e v a l v e s a r e a d j u s t e d , an a c t i o n w h i c h f o c u s e s a t t e n t i o n on t h e n e x t burner and one w h i c h l o w e r s optimum oxygen l i m i t s . An example of a f a u l t d i a g n o s t i c r u l e s i s : action(very_high,ok,_,l). w h i c h comes i n t o e f f e c t when t h e oxygen r e a d i n g i s c l a s s i f i e d as v e r y h i g h and t h e carbon monoxide r e a d i n g as O.K. No a c t i o n i s t a k e n i n t h i s case b u t a message w i l l be g e n e r a t e d by t h e a s s o c i a t e d r e p o r t c l a u s e t o t h e e f f e c t t h a t t h e oxygen s e n s o r s h o u l d be checked. One of t h e c h a i n s o f c o n t r o l r u l e s i s : a c t i o n ( h i g h , h i g h , 1 ) :- n e x t _ b u r n e r , reduce_air. action(high,high,pos,2)

:- i n c r e a s e _ i n c r e m e n t , increase_air, reduce_increment.

a c t i o n ( h i g h , h i g h , n i l , 3 ) :- r e d u c e _ a i r . w h i c h f i r e s u c c e s s i v e l y i f , i n i t i a l l y , b o t h oxygen and carbon monoxide r e a d i n g s a r e h i g h and t h e n , a f t e r t h e a i r i n l e t v a l v e t o whe burner b e i n g f o c u s e d on i s c l o s e d somewhat, t h e r e i s a p o s i t i v e change i n t h e c a r b o n monoxide r e a d i n g and t h e n , a f t e r t h e a i r i n l e t v a l v e has been opened somewhat more, t h e r e i s a n e g l i g i b l e change i n t h e carbon monoxide r e a d i n g r e t u r n i n g t h e a i r i n l e t v a l v e t o i t s original position. Rule-Based O p t i m i s a t i o n o f a S i m u l a t i o n The S i m u l a t o r . A computer s i m u l a t o r o f m u l t i p l e burner i n s t a l l a t i o n s ( 1 7 ) , r e p r e s e n t s each burner i n an i n s t a l l a t i o n by a number o f " p e r f e c t " b u r n e r s , each coded as a PROLOG f a c t , whose a t t r i b u t e s a r e d i s t r i b u t e d w i t h i n a g i v e n range t o model a p a r t i c u l a r k i n d o f burner. A l t e r a t i o n s t o t h e a i r i n l e t v a l v e s a r e r e p r e s e n t e d by changes t o t h e s e a t t r i b u t e s , as a r e changes i n f i r i n g l e v e l and s m a l l changes i n t h e b u r n e r s over t i m e . Readings a r e averaged f u n c t i o n s o f t h e a t t r i b u t e s based on e x p e r i m e n t s w i t h a near p e r f e c t burner ( 1 8 ) and t h e g i v e n c h a r a c t e r i s t i c o f a i r i n l e t v a l v e s . The S i m u l a t i o n . A s i m u l a t i o n o f a t w e l v e burner f u r n a c e w i t h a common f l u e was c r e a t e d . Each burner was s e t up w i t h randomly


184


g e n e r a t e d average e x c e s s a i r l e v e l s o f between - 5 % and 95% w i t h i t s a i r i n l e t v a l v e f u l l y open and between -25% and 2% w i t h i t s a i r i n l e t v a l v e c l o s e d as f a r as i t would go. The p a r t i c u l a r model g e n e r a t e d i s shown i n F i g u r e 2. Each v a l v e can be c l o s e d from 0% t o 100% o f p o s s i b l e c l o s u r e and t h e s i m u l a t i o n r e d u c e s t h e l e v e l o f e x c e s s a i r


burner number

excess a i r l e v e l closed open

excess a i r l e v e l open closed

burner number

1.

-5%

58%

7.

-16%

44%

2.

-19%

58%

8.

-20%

66%

3.

-10%

11%

9.

-24%

29%

4.

-19%

73%

10.

-8%

16%

5.

-13%

50%

11.

-3%

3%

6.

-24%

77%

12.

-2%

32%

F i g u r e 2. The randomly g e n e r a t e d model t o t h a t p a r t i c u l a r b u r n e r by an e x p o n e n t i a l f u n c t i o n o f t h a t p e r c e n t a g e o f t h e d i f f e r e n c e between t h e maximum and minimum l e v e l s of e x c e s s a i r t o t h a t b u r n e r . Oxygen and carbon monoxide r e a d i n g s f o r each b u r n e r a r e t h e n produced a c c o r d i n g t o t h e s i m p l e c h e m i c a l e q u a t i o n s , ( p l u s o r minus randomly g e n e r a t e d i n t e r f e r a n c e f a c t o r s ) , and t h e s e a r e averaged o v e r t h e t w e l v e b u r n e r s t o g i v e s i n g l e , f i n a l , oxygen and carbon monoxide r e a d i n g s .

Run

Initial Valve Positions

F i n a l Valve Positions 1

2

3

4

5

6

7

8

9

10

11

12

A.

0,

93, 76, 64, 80, 80, 77, 74, 77, 61, 69, 75, 96

B.

90,....

93, 76, 64, 80, 80, 77, 74, 77, 61, 69, 75, 96

C.

75

94, 76, 64, 80, 80, 77, 74, 77, 61, 69, 75, 96

D.

60,

93, 76, 64, 80, 80, 77, 74, 77, 61, 69, 75, 96

E.

0,90...

93, 76, 60, 80, 80, 77, 74, 78, 56,

F.

90,0...

93, 76, 64, 80, 80, 77, 74, 77, 61, 69, 92, 94

F i g u r e 3.

73, 58, 96

Rulebased o p t i m i s a t i o n o f t h e s i m u l a t i o n

Optimisation of the Simulation. The f i n a l v a l v e p o s i t i o n s a r r i v e d a t a f t e r r u n n i n g t h e r u l e b a s e d o p t i m i s a t i o n program on t h e s i m u l a t i o n from a number o f i n i t i a l v a l v e p o s i t i o n s a r e shown i n F i g u r e 3.


14.

FOGARTYETAL.

Optimizing Combustion in Multiple-Burner Installations 185 n

n

I n i t i a l v a l v e p o s i t i o n N , . . . i n d i c a t e s t h a t each v a l v e i s s e t t o p o s i t i o n N, w h i l e i n i t i a l v a l v e p o s i t i o n "N,M,. i n d i c a t e s t h a t v a l v e s were s e t , a l t e r n a t e l y , t o p o s i t i o n s N and M, where N and M a r e percentages o f p o s s i b l e c l o s u r e . There i s a h i g h c o r r e l a t i o n between t h e f i n a l v a l v e p o s i t i o n s s t a r t i n g from t h e d i f f e r e n t i n i t i a l c o n d i t i o n s . I n f a c t o n l y one v a l v e shows a marked d i f f e r e n c e , t h i s b e i n g t h e one f o r burner 11. I t c a n be seen from F i g u r e 2 t h a t a l t e r i n g t h e a i r i n l e t v a l v e f o r burner 11 can make v e r y l i t t l e d i f f e r e n c e t o t h e amount o f e x c e s s a i r r e a c h i n g t h a t burner anyway. M


Rule-Based O p t i m i s a t i o n o f a Twelve B u r n e r Zone o f a Furnace The Hardware. Having been d e v e l o p e d , t r i e d and t e s t e d on s i m u l a t i o n s of m u l t i p l e burner i n s t a l l a t i o n s , t h e r u l e b a s e was t h e n r u n on h a l f o f a t w e n t y - f o u r burner zone o f a 108 burner f u r n a c e on a c o n t i n u o u s a n n e a l i n g l i n e f o r r o l l e d s t e e l . The program r a n i n c o m p i l e d Turbo P r o l o g on an IBM PC XT c o n n e c t e d t o a T h i n k l a b 32 c h a n n e l A/D and 24 c h a n n e l D/A c o n v e r t e r . T h i s o p e r a t e d e l e c t r i c a l l y a c t u a t e d a i r i n l e t v a l v e s on e i g h t o f t h e b u r n e r s v i a a u n i t y v o l t a g e g a i n c u r r e n t a m p l i f i e r . The m o n i t o r e d s i g n a l s were from a z i r c o n i a oxygen probe and thermocouple i n t h e common f l u e and an i n f r a - r e d a b s o r p t i o n c a r b o n monoxide a n a l y s e r w i t h a sample p o i n t i n t h e common f l u e . O p t i m i s a t i o n o f t h e Furnace. I n i t i a l performance o f t h e r u l e b a s e was h i g h l y e r r a t i c due t o t h e i r r e g u l a r i t y o f t h e c a r b o n monoxide r e a d i n g s . I n s t e a d o f a c o n s t a n t r e a d i n g c o r r e s p o n d i n g t o each s e t o f v a l v e p o s i t i o n s t h e r e was a n o i s y band o f r e a d i n g s w i t h random peaks above i t . The n o i s e was due m a i n l y t o t h e v o l a t i l i t y o f t h e combustion p r o c e s s a t near o p t i m a l a i r / f u e l r a t i o s w h i l e t h e peaks were induced by changes i n f i r i n g l e v e l s o f o t h e r zones i n t h e f u r n a c e . T h i s problem was c i r c u m v e n t e d by w r i t i n g i n t o t h e i n t e r f a c e module, s t a t i s t i c a l p r o c e d u r e s t o f i l t e r t h e s i g n a l from t h e c a r b o n monoxide a n a l y s e r w i t h t h e consequent l e n g t h e n i n g o f r e s p o n s e t i m e and l o s s o f some i n f o r m a t i o n . The c o n s t a n t system parameters used by t h e r u l e b a s e had t o be l e a r n e d b e f o r e i t c o u l d be r u n s a t i s f a c t o r i l y . Upper and lower c a r b o n monoxide optimum l i m i t s and maximum and minimum increments f o r t h e a i r i n l e t v a l v e s a l l needed a d j u s t i n g . The r u l e b a s e c o n t a i n s no r u l e s r e g a r d i n g t h e d e t e c t i o n o f and a c t i o n t o be t a k e n i n t h e c a s e o f t h e changing o f f i r i n g l e v e l s . The f u r n a c e has o n l y one f i r i n g l e v e l f o r each zone and a c o n t r o l system m a i n t a i n s t h e r e q u i r e d t e m p e r a t u r e by t u r n i n g zones on and o f f as necessary. A l l t h e r u l e b a s e had t o a c h i e v e was t o o p t i m i s e one zone when i t was f i r i n g . I f t h e f i r i n g l e v e l changed d u r i n g a c h a i n o f rules t h i s d i d not r e g i s t e r . The program was r u n 14 t i m e s i n a l l u s i n g v a r i o u s parameters and d i f f e r e n t i n i t i a l c o n f i g u r a t i o n s o f a i r i n l e t v a l v e s e t t i n g s . On each o c c a s i o n s t a c k l o s s , a measure o f energy wasted i n t h e e x h a u s t gases a s a p e r c e n t a g e o f energy s u p p l i e d i n t h e f u e l , was reduced t o about 15%. T h i s compares w e l l w i t h t h e s t a c k l o s s o f 20% r e g i s t e r e d when t h e system was n o t b e i n g used. On each r u n v a l v e s were c l o s e d by c e r t a i n amounts and an optimum was a r r i v e d a t , b u t t h e r e was no c o r r e l a t i o n between t h e f i n a l c o n f i g u r a t i o n s o f v a l v e s e t t i n g s even when t h e same parameters were used.


186



A System w h i c h L e a r n s i t s own R u l e s The Need t o L e a r n . No c o n c l u s i o n s were r e a c h e d as t o how r e s p o n s i v e t h e r u l e b a s e w i l l be as r e g a r d s l o n g term change i n an i n s t a l l a t i o n but i t was u n a b l e t o cope w i t h s h o r t term change i n t h e form o f t h e r a p i d l y v a r y i n g c a r b o n monoxide r e a d i n g s . I t was o b v i o u s l y u n a b l e t o i n i t i a l l y adapt t o and l e a r n about t h e p a r t i c u l a r p l a n t on w h i c h i t was i n s t a l l e d and i t w i l l always need an e x p e r t t o i n i t i a l i s e and possibly maintain i t . When t h e r u l e b a s e i s used on a b o i l e r p l a n t i t may n o t be equipped t o d e a l w i t h t h e c o n s t a n t l y c h a n g i n g f i r i n g l e v e l s t h a t t h e b o i l e r s undergo. I n common w i t h most E x p e r t Systems i t p e r f o r m s l i k e a competent n o v i c e i n s t e a d o f l i k e a r e a l e x p e r t who exchanges h i s / h e r c u r r e n t knowledge f o r t h e o p p o r t u n i t y t o work on problems from w h i c h t h e y can l e a r n more ( 2 0 ) . I d e a l l y , a system t h a t l e a r n s i s r e q u i r e d : one t h a t l e a r n s t h e i n d i v i d u a l c h a r a c t e r i s t i c s o f t h e p l a n t on w h i c h i t i s i n s t a l l e d ; one t h a t l e a r n s i t s own r u l e s when i t meets s i t u a t i o n s t h a t i t e i t h e r has n o t met b e f o r e o r was n o t p r e p a r e d f o r by t h e e x p e r t s t h a t s e t i t up; one t h a t l e a r n s s i m p l e r u l e s o f t h e same format t h a t a r e e a s i l y m o d i f i a b l e a c c o r d i n g t o changing c i r c u m s t a n c e s . A S i m p l e L e a r n i n g System. A l e a r n i n g system, based on a g e n e t i c a l g o r i t h m (21), w h i c h g e n e r a t e s , t e s t s and improves a r u l e f o r o p t i m i s i n g combustion i n m u l t i p l e b u r n e r i n s t a l l a t i o n s u s i n g s i m u l a t e d e v o l u t i o n has been d e v e l o p e d . The system randomly g e n e r a t e s 50 r u l e s o f a g i v e n format and e v a l u a t e s them on a s i m u l a t i o n of a m u l t i p l e burner i n s t a l l a t i o n . I t t h e n chooses 50 t i m e s from t h o s e r u l e s , based on t h e i r performance (some w i l l be d u p l i c a t e s and some w i l l n o t be c h o s e n ) , and, u s i n g t h e g e n e t i c o p e r a t i o n s o f c r o s s o v e r and m u t a t i o n , g e n e r a t e s 50 new r u l e s f o r e v a l u a t i o n . T h i s p r o c e s s i s c o n t i n u a l l y r e p e a t e d and t h e system converges on t h e b e s t r u l e i t can f i n d . E x p e r i m e n t s have been conducted t o compare t h e performance o f t h e r u l e b a s e and t h e g e n e t i c l e a r n i n g system i n d e a l i n g w i t h n o i s e . Ten d i f f e r e n t s i m u l a t i o n s o f m u l t i p l e b u r n e r f u r n a c e s were s e t up and t h e s i g n a l s from them d i s t o r t e d u s i n g f o u r d i f f e r e n t n o i s e l e v e l s from none t o h i g h . The r u l e b a s e and t h e g e n e t i c l e a r n i n g system were used t o o p t i m i s e each o f t h e s i m u l a t i o n s a t each n o i s e l e v e l . I t was found t h a t a l t h o u g h t h e performance o f t h e r u l e b a s e i s s u p e r i o r when t h e r e i s no n o i s e , i t d e t e r i o r a t e s c o n s i d e r a b l y and p r o p o r t i o n a l l y as t h e l e v e l o f n o i s e i s i n c r e a s e d . The performance o f t h e g e n e t i c l e a r n i n g system, on t h e o t h e r hand, was t h e same no m a t t e r what t h e l e v e l o f n o i s e . The performance o f t h e two systems was a p p r o x i m a t e l y comparable a t t h e low n o i s e l e v e l . These r e s u l t s form t h e b a s i s f o r t h e development o f a l e a r n i n g c l a s s i f i e r system (22,23) f o r combustion c o n t r o l i n m u l t i p l e b u r n e r installations. Conclusion P r o v i d e d i t i s used under u s u a l c o n d i t i o n s w i t h t h e s o r t o f d a t a e x p e c t e d t h e E x p e r t System p e r f o r m s as w e l l as a human e x p e r t . I t has t h e added advantage o f b e i n g a b l e t o do t h i s 2A h o u r s a day, 7 days a week and n o t j u s t e v e r y 6 months. On t h e o t h e r hand two weaknesses can be i d e n t i f i e d . F i r s t l y , a human e x p e r t has t o l e a r n some s p e c i f i c parameters c o r r e s p o n d i n g t o c h a r a c t e r i s t i c s o f t h e


14.

FOGARTYETAL.


p a r t i c u l a r i n s t a l l a t i o n i n o r d e r t o e q u i p t h e r u l e b a s e w i t h them. Secondly, t h e rulebase i s b r i t t l e i n t h e face o f n o i s y data. I n g e n e r a l , i t i s n o t known how w e l l t h e E x p e r t System w i l l p e r f o r m i n u n u s u a l o r unexpected c i r c u m s t a n c e s . A t p r e s e n t t h e E x p e r t System c a n o n l y l e a r n by b e i n g t o l d , i . e . by h a v i n g new o r r e v i s e d r u l e s e n t e r e d by an e x p e r t . I n o r d e r t o make i t more r o b u s t o t h e r ways o f l e a r n i n g need t o be i n t r o d u c e d . The g e n e t i c a l g o r i t h p r o v i d e s one approach t o l e a r n i n g c o n t r o l r u l e s f o r t h e system and t h i s i s b e i n g v i g o r o u s l y pursued. Acknowledgement


T h i s work was s u p p o r t e d by a c o - o p e r a t i v e award from t h e S c i e n c e and E n g i n e e r i n g R e s e a r c h C o u n c i l and B r i t i s h S t e e l . (Award No.86518692).

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Slevin, M . J . : Boiler oxygen trim control. Heating/Piping/Air Conditioning, pp.95-98, November 1984. Coe, D.: Improving small boiler combustion control. Control and Instrumentation, pp.33-35, March 1987. Presser, C. and SemerJian, H.G.: Evaluation of Industrial Combustion Control Systems, U.S. Dept. of Energy, 1984. McFadden, R.W.: Multiparameter trim: it pays in combustion control, InTech, pp.57-61, May 1984. Sunderland, R.H.: Improving combustion efficiency by multivariable analysis and control, Measurement + Control, Volume 18, July/August 1985. Langridge, S.: Combustion control in process heaters, Control and Instumentation, pp.37-39, March 1987. Cremer, C. and Hertz, J.: A fast control algorithm for near optimal control of industrial combustion, Proceedings of Control-88 Oxford, IEE, 1988. Zadah, L.A.: Outline of a new approach to the analysis of complex systems and decision processes, IEEE Trans on Sys, Man and Cybernetics, vol 3, no 1, pp.28-44, Jan 1973. Mamdani, E . H . , Efstathiou, H.J. and Sugiyama, K . : Developments in fuzzy logic control, 23rd. Conference on Decision and Control, pp.888-893, Dec 1983. Efstathiou, J.: Knowledge based systems for industrial control, Comp. Aided Eng. Journal, pp.7-20, Feb 1987. Sargeant, R.A.E.: Expert systems for process control rooms, Measurement + Control, pp.239-244, Nov 1986. Jeffreys, S.: Software simplifies batch control design, Control Engineering, pp.107-109, Sep 1987. Highham, E . H . : A different approach to self tuning in process controllers - the case for introducing an expert system, Meas. and Control, vol.19, pp.253-257, Nov 1986. Francis, J.C. and Leith, R.R.: Artifact: A real-time shell for intelligent feedback control, in Research and Development in Expert Systems, M. Braemer (Ed), 1985. Darius, I . H . : Rule based control, a new tool, Proc.2nd Int.Conf.Machine Control Systems, pp.121-128, May 1987.



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16. Edmundson, J . T . , Jenkins, D.P. and Mortimer,J.: Multiple Burner Stoichiometry Control in Innovation in Process Energy Utilisation, IChemE, pp 47-60, 1987. 17. Fogarty, T.C.: A Prolog Simulator for Combustion Control, Bristol Polytechnic Technical Report, 1987. 18. Wakefield, A.A.: An Expert System for Methane Flame Stoiciometric Control, MSc Diss., Bristol Polytechnic, 1986. 19. Gaines,B.R.: How Do Experts Aquire Expertise?, Proc. of AAAI Workshop on Knowledge Aquisition for Know.-Based Systems, 1987. 21. Holland,J.H.: Adaption in Natural and Artificial Systems, 1975. 22. Holland,J.H.: Escaping Brittleness: The Possibilities of General Purpose Learning Algorithms Applied to Parallel Rule-Based Systems, Machine Learning; An Artificial Intelligence Approach, Volume 2, eds. Michalski, Carbonell, Mitchell, pp 593-623, 1987. 23. Wilson,S.W.: Classifier Systems and the Animat Problem, in Machine Learning, vol.2, no.3, pp 199-228, 1987. RECEIVED June 9, 1989


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