FIGURE 9 Production of methanol from natural gas (steam reforming).
Higher alcohols and purge gas
'I
1
METHANE STEAM METHANOL SYNTHESIS
REFORMING gas compression
464x1
o6
PJm31ymethanol synthesis product distillation
4
CARBIDE-OVEN GAS
I
Higher alcohols and purge gasNATURAL GAS
1
LMETHANE STEAM W METHANOL SYNTHESIS
REFORMING gas compression
methanol synthesis
440x 1
o6
~ m ~ / y product distillationI I
Waste waters
+
METHANOLFIGURE 10 Production of m e t h a n o l f r o m n a t u r a l g a s a n d (CO-containing) gases from carbide ovens ( s t e a m reforming).
1
Higher alcohols and purge gasNAPHTHA
1
NAPHTHA STEAM METHANOL SYNTHESIS
REFORMING '
gas compression
I methanol synthesis
I I .
product distillationWaste waters
+
METHANOL-
500000 t/v
FIGURE 11 Production of m e t h a n o l from n a p h t h a ( s t e a m reforming).
AIR FIGURE 12 Production o f rnet.hano1 from coal (Koppers-Totzek process).
gas compression a methanol synthesis
product distillation Higher alcohols
O2
b AIR SEPARATION A
A
Vent gas Steam b
COAL
GASIFICATION
SULFUR RECOVERY Claus plant TGT
b - b ACIDGAS WASHING
coal prep.vation C02
coal gasification 1 . 5 ~ lo6 t/y heat -ecovery
treatment of wastes b
and by-products
GAS PREPARATION
-
co2partial oxidation heat recovery
Wastes and by-products C 0 2 washing
ash
ammonia
I
bphenol 0 m h'
oil al P METHANOL SYNTHESIS
waste waters &
Sulfur
Waste waters gas compression
4 methanol synthesis
product distillation
1 v
Higher alcohols METHANOL
500000 t l y FIGURE 13 Production of methanol from coal (Lurgi ~ r o c e s s ) .
FIGURE 14 Production of nlethanol from coal (Lurgi process, SNG production, and steam reforming).
I
b AIR SEPARATION
:
SULFUR RECOVERYClaus plant
TGT Sulfur
Steam
1
0 2COAL L
b 1 .897xlo6 t/y
GAS1 F ICATION coal preparation coal gasification heat recovery treatment of wastes and by-products
I
GAS PREPARATION shift conversion heat recovery
ACID GAS WASHING
I
METHANATION tmethanation heat recovery Wastes and by-products
Higher alcohols and purge gas
I
ash
I *
ammonia
1
'IREFORMING OF METHANE w phenol
oil waste waters
product distillation
1
a
+
METHANOL
- 1-
Waste waters 500000 t/y
METHANOL SYNTHESIS gas compression methanol synthesis
4.3 Results of Simulation Experiments
What we have actually done in the case of methanol is to carry out a comparative study of various production technologies. Two factors are emphasised: financial efficiency and investment. In order t o make the analysis independent of the value of t h e discount r a t e and t h e corresponding t i m e horizon, financial efficiency and investment should be treated i n a way t h a t reveals the properties of the PDA with these two factors taken as objec- tives. Here we define financial efficiency as the n e t yearly financial flow for t h e whole PDA, i.e., t h e difference between the value of the resources obtained from the PDA and the value of the resources consumed in produc- tion. This gives some indication of the value added, and opens the way to f u r t h e r economic analysis.
This approach is illustrated by t h r e e examples. Although we come back to t h e results obtained in these experiments i n more detail in the section dealing with methodology, it is worth noting h e r e t h a t this methodology is designed to help t h e decision maker find out what is "the best" t h a t can be attained from a given PDA.
Further evaluation of the individual investment projects can be per- formed using t h e standard tools of microeconomic analysis (discount rates, r a t e s of r e t u r n , n e t present values, e t c . ) .
Case 1. Maximization of eficiency u n d e r constraints on investment
In this case we a r e looking for t h e combination of methanol production technologies t h a t maximizes efficiency a t different fixed levels of investment.
It is assumed t h a t t h e r e are no constraints on t h e availability of raw materi- als. Table 6 gives a summary of the results obtained a t five different fixed investment levels, together with the corresponding efficiency/investment ratios (Experiments 1-5). The solution is given in t e r m s of the total amount of each raw material consumed, together wlth the corresponding energy con- sumption and methanol production levels. Table 7 shows how this consump- tion of raw materials relates to t h e levels of use of t h e individual production processes; the values a r e given in t e r m s of t h e percentage utilization of installed capacity. These figures give some idea of t h e order in which the vari- ous processes should be introduced as investment is increased, and may also be used to draw conclusions about economies of scale.
Thus, for a given s e t of constraints and objective function, this type of analysis can yield information on
-
the order in which different raw materials should be used for methanol production;-
the order in which the individual production processes should be intro- duced;-
the levels of methanol production a n d resource consumption;- t h e performance of the industry a s compared with others (as reflected i n the efficiency/inves tment ratio).
TABLE 6 Maximization of efficiency u n d e r c o n s t r a i n t s on investment. availability of natural gas. The various situations considered are summarized in Table 8. In experiments 1 and 7 we examine t h e effect of reducing the avai- lability of natural gas t o zero, with investment limited t o 20x10' m . u . in both cases. We find t h a t the lack of natural gas in experiment 7 leads to a dramatic drop in methanol production compared with the control experiment ( I ) , and t h a t energy consumption rises markedly (by a factor of 2.5). The substitution of raw materials and processes caused by t h e nonavailability of natural gas is shown clear!y in Table 9. In experiments 8 and 9 we again examine t h e effect of reducing the availability of natural gas to zero, b u t t h i s time with the
constraints on investment replaced by constraints on energy consumption.
We again find a spectacular decline in methanol production in the zero natural gas situation (experiment 9); Table 9 shows t h a t production from natural gas in experiment 8 (the control experiment) is replaced entirely by production from coal in experiment 9.
TABLE 8 Maximization of efficiency under constraints on investment, energy con- sumption and natural gas availability.
Efficiency/investment ratio 0.47 0.34 0.40 0.33
ONot limited - see below.
'~imited
-
see above.TABLE 9 Utilization of methanol production processes (as a percentage of installed capacity) corresponding to the solution giver1 in Table 8.
- efficiency and investment, lie simultaneously within certain admissible ranges. This is one way of treating the problem of "concordance". Table 10