計測自動制御学会東北支部 第 209 回研究集会 (12 June 2003)
資料番号 209-10

物質およびエネルギーの変換を考慮し た
バッチプラント の運転操作手順生成手法
Synthesis of Operating Procedures for Material and Energy Conversions
in a Batch Plant◯金子 陽一郎 ∗ , 山下善之 ∗ , 星 憲司 ∗∗◯ Yoichiro Kaneko∗ , Yoshiyuki Yamashita∗ and Kenji Hoshi∗∗∗∗

東北大学大学院工学研究科, ∗∗ 東北薬科大学

Tohoku University, ∗∗ Tohoku Pharmaceutical University

キーワード : 操作手順生成 (Synthesis of Operating Procedures), 部分グ ラフ同型 (subgraph-isomorphism),
シーケン ス制御 (sequence control)

連絡先 : 〒 980-8579 仙台市青葉区荒巻字青葉 07 東北大学大学院工学研究科 化学工学専攻
e-mail: {k-yoichi |yyama}@pse.che.tohoku.ac.jp

1.

Abstract
The problem of operating procedure synthesis

Introduction

A sequence of unit operation is required to pro-

Knowledge

duce target products in a given batch plant. The

about plant structure and material-conversion pro-synthesis of the sequence can be defined as search-cedures was represented by directed graphs and theing allowable sets of sequential operations and an

subgraph-isomorphism algorithm was utilized toinitial state to realize a given final state without

solve the problem. The concept of heat-resources

violating constraints. This problem is a complex

is introduced here as an extension of usual equip-problem and usually designed by human expert.

ments. A mechanism to have multiple outputs forIn these days, small quantity and multi-purposea material conversion is also proposed. These ex-

production become popular and the generation ortensions provide the method to deal with the op-changes of operating procedures become frequent.

eration of heat exchange and separation for theOperating procedures are usually generated by hu-synthesis of operating procedures in our subgraph-

man experts and it requires considerable amountisomorphism framework. The method is success-of time and efforts.

fully applied to a double effect evaporator.

matic generation of operating procedures is get-for process plants is investigated.

The requirement of auto-

T1

V4
Feed Tank

ReactorT1

T3

V1
Mixing Tank

.

T2

T3

Step 1
Step 2V2
V3

Step 3

T2

Step 4SteamPU1....

V4V5Fig. 1

The example plant and corresponding sequential plant-structure graphting increased to improve the efficiency. It is alsoeffect evaporator plant to generate operating pro-required to verify the generated operating proce-cedures.

dures for the improvement of the reliability and thesafety.

2.

MethodSeveral approaches have been investigated for
To generate a sequence of operating procedures

the automatic synthesis of operating procedures ofa chemical plant. Viswanathan et al. proposed a
synthesis method based on the Grafset, a discrete
event model concept1) . Aylett et al. applied AI
planning tool to the synthesis of operating procedures of a chemical plant2) . We have proposed
directed graph representations and recursive algorithm to solve this problem3, 4) . Recently, we introduced a subgraph isomorphism framework tothis problem domain5) . Short summary of the sub-for a production of a specific product by a given
plant, the knowledge about connectivity of plant
equipments and the knowledge about operations
for material conversions and energy conversions
are required at least.

2.1

Plant Structure

In this study, the connectivity of plant equip-graph isomorphism framework will be described inments is represented as a digraph named sequential plant-structure graph3) , which can also deal

section 2.

with state transitions of the plant. For example, aIn this paper, our subgraph isomorphism frame-simple example plant shown in Fig. 1 is converted

work is extended so as to deal with heat exchanges

into the sequential structure-graph are shown in theand chemical separations. For these purposes, theright side of the figure. In this representation, eachconcept of heat resources is introduced as the ad-nodes represents process equipment and each di-dition of material-conversion graph. Moreover, therected arcs represents the direct connectivity be-

output from one node is extended to have multi-tween equipments. Here, valves and pumps areple materials in the material-conversion graph. Fi-

implicitly included in the arcs. For example, arcs

nally, the method is demonstrated on the double-

from T1 to T2 include valves V1 and V3, and arcs

–2–

name
UP1
UP2
UP3

typeconversion
procedures
A→B
C→D
B+D →E

Reaction
Reaction
Mixingequipment
constraints
T2
T2
T1,T2,T3

B

UP1A

UP3

DUP2

CFig. 2

Unit operations for material conversions and the material-conversions graph

T1T2A

T3

T1C

Step 1

UP2

Step 2AT2

T3

Step 1UP2

Step 2

Steam

Step 4

UP33

Step 5

Step 3

Step 4UP1’UP33

E(a) without heating

Fig. 3

SteamSourceC

Step 3

UP1E

Step 5E(b) with heating

One of the feasible operating procedures to produce E in the example plantfrom T2 to T3 include PU1 and V4. Each lines

resent raw materials and the goal point is the targetof the graph is corresponding to a time step, which

product E. Other nodes represent a sequence ofduration of time is not constant. Nodes in the same

unit operations to convert the connected materials.

column are the same equipments in different time

The materials B and D, those are produced by unitsteps. Each arcs represents a material flow be-

operations UP1 and UP2, are implicitly included intween the connected equipments. Arcs connected

the arcs to the node UP3.

to the same equipment represent the state of holding the contents in the same equipment.

2.3 Synthesis by Subgraph Isomorphism
The synthesis of operating procedures to pro-

2.2 Material Conversion Procedures

duce a target material is the task to find path of
The knowledge about unit operating proceduresmaterial conversions from raw materials to the tar-and material conversions is represented by digraphnamed material-conversion graph1) . For example,

get materials and to allocate the each conversion

the knowledge about unit operating procedures andlem is to find out if the plant-structure graph con-material conversions listed in the left side of Fig. 2

tains a subgraph that is isomorphic to the material-is converted into the material-conversion graph as

conversion graph, or find all such isomorphic sub-shown in the right side. Here, the start points rep-graphs. Cordella et al. have developed an efficient

procedures on a specific equipment. This prob-–3–Steam
name
UP1’

type

procedures

Reaction& Heating

equipment
constraints
T2

A + (Heat) → B

UP1’A

D

UP3

E

UP2

CFig. 4B

A modified procedures for material and energy conversions

name

type

procedures

UP4

separation

X→Y +ZY

equipment
constraints
T3

X

UP 4ZFig. 5

Example of a separation operation

algorithm for graph-subgraph isomorphism6) . We

heat exchanges in process plants are using such

implemented the algorithm with special consideration to solve this problem5) .

utility lines as steam and water,
By using this definition, the subgraph isomor-Applying to the practical problem, many kinds

phism algorithm can be used to generate the op-of restrictions must be considered to get the appro-erating procedures for a plant including energy

priate procedures. Typical restrictions for chemi-conversions. An example of material-conversion

cal plants are avoidance of contaminations, possi-graph including energy conversions is shown in

ble equipments for a specific operation, and so on.

Figure 4. Figure 3(b) shows an example of op-In this study, these restrictions are treated as theerating procedures for the example plant. In thisconstraints during the search of the solutions. Fig-figure, a line from Steam to UP1’ provides steam

ure 3(a) shows one of the feasible solutions of thefrom the heat source to the tank T2, then the UP1’

operating procedures to produce E.

operation convert the material A to B.

2.4

2.5

Energy Conversion Procedures

To deal with unit operations such as the heat exchange, conversion and transfer of the energy must
be considered. Let us consider about the jacket
heating in Fig. 1. In this example, the first unit
operation is replaced to a reaction with heating byconsidering about the heating (Fig. 4). The material conversion is the same but the term (Heat)in the conversion procedures is introduced here.
This term means that the operation includes heatexchange, and requires a heat source. The source

Separation Procedures

Separation operation did not treated in the previous study5) , because each nodes in the materialconversion graph has only one output arc. In thisstudy, this restriction is removed to have multiple
output arcs from one node. Implementation of thegraph-subgraph matching was improved to satisfy
this functionality. As the result, separation operation can be treated in the same framework. The
node UP4 in Fig. 5 shows an simple example ofthe material conversion with separation operation.

of utilities are also introduced, because most of the–4–

3. Case Studygraph shows material transfer, where the operationof valves and pumps are implicitly included. The

To demonstrate the ability of the proposed algorithm, the synthesis of operating procedures for thestart-up of a double-effect evaporator2) is investigated here. Figure 6 shows the schematic flow of
the target plant. The purpose of this plant is to remove water from a salt water solution. This plantis called double-effect, because the steam that isevaporated off from the salt-water solution in thefirst evaporation is used to supply the energy forthe second evaporation.

matched graph can be easily interpreted to a sequence of operations as shown in Table 2. In thistable, operations such as evaporation and heating
are corresponding to the nodes having the nameof unit operations in the matched graph. Activation of valves and pumps are corresponding to thearcs in the graph. Initially, all the valves are supposed to be closed and no pumps are working. After completed operations in each steps, each valvesmust be closed to move to the next step, if it is

In this plant, the salt water SW is fed from theopened again in the step. Final lines in steps 3, 5

feed tank FT, preheated in Glass Heater GH andand 8 do not require any valve operations, because

heated in Heat Exchanger HE1, and evaporated inthe equipments are connected directly without any

the first stage evaporator EV1. The steam ST gen-valves. The initiation time and condition of eacherated by the first stage evaporator is used as a heat

operation steps are not considered.

source in the second stage evaporator EV2. The
By watching this operating procedures, the se-separated liquid LQ1 in EV1 is heated in HE2,and evaporated in EV2. Finally, steam is collectedby barometric condenser BC1, then water W T is
obtained in tank TK2, and liquid product LQ2 isquence of operations seems very reasonable. The
operation of double effect is also realized by thetransfer in step4. Although the algorithm could
generate many possible solutions, the selection ofobtained in tank TK1.

appropriate solution will be the future work.
This plant includes heat exchangers and evaporators, which requires both the material flow andthe energy flow. Material and energy conversion

4.

Conclusion

procedures for this plant is described in Table 1. In
this table, UP1, UP2 and UP4 are the operation for

A subgraph-isomorphism framework for theheating, and UP6 are the operation for cooling.

synthesis of operating procedures for chemical

By representing the plant structure as the struc-plant is extended to deal with the operations of heat

ture graph (Fig. 7), material and energy conver-exchange and separation. This extension enables

sion procedures as the conversion graph (Fig. 8),

the consideration of operations related to the util-

the proposed algorithm was applied to generate theities such as steam and process water for various

operating procedures. Figure 9 shows an example

plants. The proposed method was demonstrated onof the generated matched graph representing thethe double-effect evaporator plant and confirmedoperating procedures to produce the target productthat it generates very reasonable operating proce-LQ2 in TK1 and W T in TK2. Each arcs in thedures automatically.

–5–V10AirPW
V21

FT

EV 1

Pump3
SteamDrain
V7V2

GHBC 1

V13

V18

V16
V14

V11

EV 2

V3Drain
V5
V8
V1

HE 1

HE 2

V9

V15

Drain
V4

SteamV12

Pump2

V6

Pump1
Drain

V19

V17

TK 1

V20

TK 2Drain

FT : Feed tank GH : Glass Heater HE : Heat Exchanger Ev : Evaporator
V : Valve TK : Tank BC : Braometric Condenser PW: Process Water
Fig. 6The double-effect evaporator (DEE)

Table 1

Material and energy conversion procedures for the case study problem

nameUP1
UP2UP3UP4UP5UP6UP7type
Preheating
Heating
Evaporation
Heating
Evaporation
Condensation
Condensation

conversion procedures
SW + (HEAT) −→ SW 0
SW 0 + (HEAT) −→ SW 00
SW 00 −→ ST + LQ1
LQ1 + (HEAT) −→ LQ10
LQ10 −→ ST 0 + LQ2
ST − (Heat) −→ W T
ST 0 − (Heat) −→ W T

References

equipment constraints
GHHE1, HE2
EV1, EV2
HE1, HE2EV1, EV2
BC1BC1Suzuki, M., KES2001, Osaka, Japan (2001).
Srini-4) Hoshi, K., Nagasawa, K. Yamashita, Y. andvasan, R., Venkatasubramanian, V. andSuzuki, M., Journal of Chemical Engineer-Ärzen, K. E., Compututers and Chemical

ing of Japan, 35 (2001) 377–383.

1) Viswanathan, S.,

Johnsson, C.,

Engineering, 22 (1998) 1673–1685.

5) Hoshi, K. Yamashita, Y. and Suzuki, M., Ka-2) Aylett, R. S., Soutter, J., Petley, G. J.,Chung, P. W. H. and Edwards, D., Engineering Applications of Artificial Intelligence, 14(2001) 341–356.

gaku Kogaku Ronbunshu, 29 (2003) 107–111.
6) Cordella, L. P., Foggia, C., Sansone, C. andVento, M., ICPR’96, Vienna, Austria (1996)

3) Hoshi, K., Nagasawa, K., Yamashita, Y. and–6–180–184.

steam

FT

steam

GH

HE1

process water

EV1

HE2

EV2

BC1

TK2

TK1

Fig. 7

Plant structure graph for the DEE plant

STST

PW
PW

SW

UP1

UP2

preheating

heatingUP3evaporation

UP4
heating

UP5

UP7

UP6

evaporation

condensation

condensation

LQ2

Fig. 8

SteamSource

WT

Material and energy conversion graph for the DEE plant

FTGHHE1

EV1

HE2

EV2

BC1

TK2

TK1

SW

Step1

UP1

Step2

UP2

Step3

UP3

Step4

UP4

Step5

UP5 UP6

Step6

WT LQ2

UP7

Step8

WTFig. 9

Step7

Step9

An example of generated procedures for the DEE plant–7–Table 2
step
step1

step2

step3
step4

step5

step6

step8

Interpretation of the generated procedures for the DEE plant

operation
Prepare salt water in FTTransfer the contents of FT to GH
Transfer steam to GH
Preheat in GH
Transfer the contents of GH to HE1
Transfer steam to HE1Heat in HE1(Transfer the contents of HE1 to EV1)
Evaporation in EV1
Transfer the vapor from EV1 to HE2
Transfer the liquid from EV1 to HE2Heat in HE2
Transfer the vapor from HE2 to BC1(Transfer the liquid from HE2 to EV2)
Evaporation in EV2
Condensation in BC1
Transfer the vapor from EV2 to BC1, then TK2Transfer the liquid from EV2 to TK1Condensation in BC1(Transfer the contents of BC1 to TK2)

–8–activation of vales or pumps
by opening V2
by opening V1
by activating Pump1, V4 andV8by opening V7

by opening V14
by activating Pump1, Pump2,V5 ,V20 and V17
by opening V16by opening V18
by opening V15