The examples of process networking described, dealt exclusively with chemical manufacturing. Yet, the types of material and energy flows found in chemical manufacturing (solvents, acids, water, energy, salts) are used in a wide variety of industrial sectors. It would, therefore, seem reasonable to consider designing industrial networks that involve a variety of industries.
One of the classic examples of this type of network is a group of facilities located at Kalundborg in Denmark. At Kalundborg, an oil refinery, a sulphuric acid plant, a pharmaceutical manufacturer, a coal burning power plant, a fish farm, and a gypsum board manufacturer form an industrial network, exchanging flows of energy and mass. As shown conceptually in Fig. 8.4, the power plant and the refinery exchange steam, gas, and cooling water.
Waste heat from the power plant is used in district residential heating and to warm greenhouses and a fish farm. Ash from coal combustion at the power plant is shipped to cement manufacturers. Calcium sulphate from the scrubbers at the power plant is sent to the gypsum board manufacturer. Treated process sludges from the pharmaceutical plant are sent to local farmers for use as fertiliser, and the refinery sends hot liquid sulphur from the desulphurisation of crude oil to a sulphuric acid manufacturer.
A more detailed examination of the exchanges of material and energy at Kalundborg reveals a number of interesting features:
1. The Ecopark developed over a period of more than 30 years. Some material and energy exchanges have occurred for decades and the exchanges continue to grow in extent.
2. The exchanges have the potential to be remarkably efficient. For example, the power plant is able to use some of the waste heat and steam produced through power generation by sending it to the refinery, greenhouses, the fish farm, and the district heating system. If markets were found for all of the waste steam, up to 90 per cent of the heat from the plant’s combustion of coal could be utilised. The only losses would be energy escaping with the stack gases. By contrast, typical coal-burning power plants in the United States use heat from combustion solely to generate electricity, at an efficiency of about 40 per cent.
3. Material and energy exchanges provide economic benefits to the participants. In some cases, such as the power plant’s sale of calcium sulphate to the gypsum board manufacturer, the direct economic benefits do not fully cover the recovery costs. In these cases, the exchanges are driven by regulations, such as those requiring the scrubbing of power plant stack gases to remove SO2. The exchanges simply lower the cost of compliance by making it unnecessary to landfill or otherwise dispose of the waste generated by the scrubbers. In other cases, such as the use of power plant waste heat in the refinery, the exchanges are self-supporting.
The central facilities in the Kalundborg Ecopark are the power plant and the oil refinery. Many of the exchanges either originate from or go to the power plant or the refinery. While using a power plant or a refinery as a central facility is a concept that could be successful in other locations, many other approaches are possible. Consider, for example, an eco-industrial park in North Texas where the central facility is a steel mill. This facility, shown conceptually in Fig. 8.5, utilises scrap cars as the primary feed material.
The steel from the vehicles goes to an electric arc furnace, producing a variety of steel products. The furnace also produces a significant quantity of electric arc furnace (EAF) dust, which contains significant quantities of zinc, lead, and other metals. In the North Texas facility, the EAF dust is sent to a cement kiln where the trace metals (copper, sulphur, manganese, chromium, nickel, zinc, lead, and others) have value. Automobile Shredder Residue can be burned for energy recovery, or some of the plastics in the residue can be separated.
Another alternative for electric arc furnace dust, currently being explored in Europe, is as a feed for zinc and lead recovery operations. The recovered zinc can then be used in producing galvanised steel products and batteries can be used as an alternative source of zinc.
These two case studies illustrate the basic principles of ecoparks—integrating flows of energy and materials in diverse industrial operations, increasing mass and energy efficiency. The two cases examined here, involved exchanges between facilities that are located adjacent to each other; however, co-location of facilities is not always necessary.