PUROX system

The Union Carbide Purox system (17) uses municipal solid waste as the feed. Shredded ferrous-free refuse enters the top of the conversion furnace and is contacted countercurrently with hot combustion gases from the reaction occurring in the hearth. 

Moll, A.J. and Clark, C.R., "An Overview of Alcohol Production Routes", presented at "Alcohols as Alternative Fuels for Ontario" Symposium, Toronto, Ontario (19 November 1976). Moses, C.T. and Rivero, J.R., "Design and Operation of the Purox System Demonstration Plant", from the 5th Nat. Congress on Waste Management Technology and Resource Recovery, Dallas, (7-9 Dec. 1976). 

Fisher, T,F., Kasbohm, M,L, and Rivero, J.R, "The PUROX System," in Proceedings 1976 National Waste Processing Conference, Boston, May 23-26, 1976, American Society of Mechanical Engineers, 1976,... 

The PUROX System, developed by Union Carbide Corporation of the U.S., pyrolyzes refuse by use of oxygen. It additionally purifies and recovers the pyrolysis gas and collects the inorganic residue in the form of slag. The wastewater generated during gas purification is discharged after treatment. There are several papers (1, 2, 3, 4 ) published on the details of the system. 

Figure 1 shows the schematic flow of a typical PUROX System. 

To meet the abovementioned local conditions, Showa Denko has established a process whereby the pyrolysis gas is directly combusted and the generated heat is utilized for evaporation and oxidation of the wastewater from the refuse pit (hereinafter called the Dry Process). The schematic flow of the Dry Process PUROX System is as shown in Figure 2. 

Using the PUROX System pilot plant of Union Carbide located at Tonawanda, New York, U. S. A., Showa Denko conducted a demonstration test on simulated Japanese refuse from June through August, 1978, after making some modifications of the plant. An overall view of the pilot plant appears in Figure 3. The purpose of the demonstration was to achieve the following three objectives. 

To conduct tests on simulated Japanese refuse and thereby collect additional data to supplement those obtained on U.S. refuse, in order to obtain the technical approval of the Ministry of Health and Welfare (MHW) of Japan for the PUROX System,... 

Figure 2. Schematic flowsheet of the dry process PUROX system...

Although the pilot plant had a refuse treatment capacity of 20 Mg/d, it was usually operated at reduced load due to limitations coming from the refuse preparation site. Also schedule constraints prevented replacement of the desuperheater and scrubber employed to clean fuel gas in the pilot plant, by a waste heat boiler and electrostatic precipitator, such as are employed in the Dry Process PUROX System design. Consequently, dust was not recycled. 

The combustor off-gas corresponds to the throughput to the gas cooler (e.g., waste heat boiler) of a commercial plant. The gas analysis is given in Table VII, The values for the conventional stoker type incinerator are those in the case of large cities in Japan. They are average values with the exception of HC1, which is slightly higher. The amounts of particulate, SOx and HC1 contained in the off-gas of the Dry Process PUROX System are much less than those of the stoker incinerator. The reason is considered to be that the Cl", SO , etc. combine with alkali metals and shift into the slag in the converter. 

Furthermore, it was confirmed that addition of limestone to the refuse as the neutralization agent reduces the volume of HC1 in the off-gas to about 60%. Further study is required, however, of the relationship between the HC1 removal rate and the amount of limestone added and of the method of such addition as well. With the exception of its particulates, off-gas from the Dry Process PUROX System can satisfy Japanese national emission and effluent standards without any special treatment. 

On the basis of the price levels as of spring 1979 and at the translation rate of 200 yen to one dollar, the construction cost of the Dry Process PUROX System in Japan is estimated to be about 13,000,000 for a 200 Mg/d facility ( 65,000 for Mg of refuse), exclusive of the land, utility supply facilities down to the battery limits, and fixtures and supplies. This is about 10% higher than the construction cost in Japan of the stoker incinerator, which is estimated to be about 58,500 per Mg of refuse. 

Table X shows the running costs of the Dry Process PUROX System as well as the stoker incinerator. In Japan solid refuse treatment plants are operated by local municipalities and taxes and depreciation are not considered components of the running costs of solid refuse treatment plants. They, therefore, comprise electricity, water, chemicals, auxiliary fuel, labor, and maintenance costs. When a comparison is made on the basis of these costs, the Dry Process PUROX System is somewhat higher than the stoker incinerator.

TABLE X. RUNNING COSTS OF DRY PROCESS PUROX SYSTEM (Design capacity 150 Mg/d)... 

Unit Price Dry Process PUROX System Stoker Incinerator ... 

Moses, C. T, Rivero, J, R., Design and Operation of the PUROX System Demonstration Plant, Fifth National Congress on Waste Management Technology and Resource Recovery, Dallas, Texas, December 1976. 

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