Abstract:
The energy analysis of the cast acrylic sheet factory whose capacity is approximately 4,200 ton per year was conducted in this study. The current average total specific energy consumption is
13,546 MJ/ton of product, which consists of 10% of electricity and 90% of bituminous coal for generating saturated steam of 2.14 ton/h at 6.5 bar. About 52% of generated steam was directly
injected into the hot-water bath for heating the acrylic solution within the mold called boiling process, and the water temperature was controlled at around 63.5 0C. Thus the energy analysis was focused on the boiling process. There are 7 water baths, all are operated as batch process.
The analysis results showed that specific energy consumption (SEC) for the whole processes which, as expected, inversely related to the production rate. It was reduced from 13,674 to 9,226
to MJ/ton of product, when the monthly production was increased from 334 to 675 ton/month, respectively. While the SEC of boiling process was in the range of 3,741 to 6,383 MJ/ton of
product for the production rate from 19.24 to 11.31 ton/day, respectively. The high energy cost, as analyzed in this study, came from the opportunity loss of condensate return of the direct
steam injection that was used in the hot water bath. To reduce the energy cost three methods of improving boiling process were proposed. The first was well production planning, if the existing
boiling process could operate at higher rate of 17.58 ton/day, the SEC could be reduced to around 4,210 MJ/ton of product. The second was heating the water bath by injection steam through
the copper pipes installed in the water baths. The discharged condensate was then returned to boiler feed tank. To maintain the water level of water baths, the makeup water was required.
The evaluation results of energy cost saving showed that in the second method with the amount of makeup water the same as existing steam injection rate of 1.1147 ton/h, the energy cost could
be reduced by 136,474 bath/y and payback period of 1.8 years. Since the water level in the bath was approximately 20 cm higher than its requirement, the makeup water could be reduced.
In the case of reducing of the exceed water level of 50%, 75% and 100%, the energy cost saving and payback period were 335,122 bath/y and 0.65 year, 444,123 bath/y and 0.48 year, and
548,848 bath/y and 0.39 year, respectively. The third method was the bath heating by using the condensate from the other processes, and we found that it could not reduce the energy cost.