Other Possible Industrial Ecosystems

Several proposals superficially comparable to the Kalundborg example have been made. One of the oldest is the 'nu-plex' concept, promoted vigorously by nuclear power advocates at Oak Ridge National Laboratory (USA) in the 1970s. It was, however, basically an idea for an industrial park for large-scale electric power consumers.

A more interesting scheme, from our perspective, is a proposal aluminum-kombinat for utilizing low-grade (high-ash content) anthracite coal to recover aluminum and cement (Yun et al. 1980). The project was conceived at the Korean Institute of Science and Technology (KIST) as a possible answer to two problems. First, the city of Seoul needed to dispose of several million metric tons of coal ash each year. At the same time, South Korea was totally dependent on imported aluminum, and there was a strong desire to become self-sufficient. After several years of investigation, the kombinat scheme evolved. As of 1980, a 60 metric ton per day pilot plant was in operation and process economics appeared to be favorable.

In brief, the energy from coal combustion would be used to generate the electric power for aluminum smelting. The inputs to the kombinat would be low sulfur anthracite coal (1.9 million metric tons per year - MMT/yr), limestone (3.9MMT/yr) and clay (0.48MMT/yr). Outputs would be 100 thousand metric tons (100 kMT) of aluminum and 3.5MMT of Portland cement. The heart of the scheme is an alumina plant, consisting of two units: a sintering plant (coal + limestone + soda ash) yielding high-temperature exhaust gases (900 °C) for the steam turbine and 2MMT/yr clinker for the leaching unit. The latter grinds the clinker and leaches the alumina with hot sodium carbonate solution. The soda combines with alumina, yielding sodium aluminate in solution, while the lime combines with silica precipitating as dicalcium silicate. The latter is sent to the cement plant. The sodium aluminate is then treated in a conventional sequence, first by adding lime to precipitate the dissolved silica and then carbonation of the solution (with CO2 from the waste heat boiler) to reconstitute the soda ash and precipitate aluminum hydroxide. When aluminum hydroxide is dehydrated (that is, calcined) it becomes alumina. About 40kMT/yr of soda ash would be lost in the soda cycle, and would have to be made up. According to calculations and test results, aluminum recovery from the ash would be about 71 per cent, while the thermal efficiency of the electric power-generating unit would only be about 15 per cent owing to the considerable need for process steam by the leaching plant, mostly for calcination. The basic scheme is outlined in Figure 5.1.

A scheme similar to the kombinat was analyzed independently in the late 1970s by TRW

480kMT/yr

Figure 5.1 Conceptual diagram of cm aluminum kombinat

480kMT/yr

Figure 5.1 Conceptual diagram of cm aluminum kombinat

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