Limestone process, capital investment

The high capital investment cost of the Asahi process is due to the necessity for large absorbers, evaporators, crystallizers, dryers, rotary kiln crackers and screw decanter separators. The major operating and maintenance costs are electricity, fuel oil, steam and chemicals such as soda ash, EDTA and limestone. The requirement for consumption of large amounts of utilities is associated with the operation principle and design of the Asahi process. According to the economic evaluation, equipment required for N0X and SO2 absorption (such as packed-bed absorbers) accounts for 20% of total direct capital investment for treatment of dithionate ion (such as evaporator, crystallizer, dryer, and cracker) it accounts for about 40% and for treatment of nitrogen-sulfur compounds (such as screw decanter and cracker) it accounts for only 2%. 

Retrofit. Use of adipic acid in an existing lime or limestone system does not require modification of process flow configuration or absorber design therefore, it is particularly suited for retrofit applications. The fact that it may be added at any point in the slurry circuit provides a greater flexibility in the location and installation of a simple solids storage and feed system, a minimal capital investment. 

The capital investment for the spray dryer MgO FGD process is 139.5M ( 279/kW) in mid-1982 dollars while that for a comparable limestone scrubbing/ESP process is 122.0M ( 244/kW) in mid-1982 dollars. The capital investment for the conventional MgO FGD process (including particulate control) is 149.7M ( 299/kW) in mid-1982 dollars. These costs are... 

The capital investment for the spray dryer MgO process is approximately 14K higher than that for the comparable limestone scrubbing process. This is not an unexpected result since the MgO process is a regenerable system while the limestone scrubbing process is a throwaway system. 

The spray dryer MgO process appears to have a slight advantage (about 10 ) over a comparable limestone scrubbing process in terms of both first-year and levelized annual revenue requirements. This new MgO process, however, has a higher capital investment than the limestone scrubbing process. 

TABLE A-I. CONVENTIONAL LIMESTONE PROCESS SUMMARY OF CAPITAL INVESTMENT... 

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