3.2.3 Incineration with heat recovery. The recovery and sale of heat as steam is economically attractive with conventional waste incineration and with high temperature slagging incinerators. Tables 8 and 9 give the economic data summary. Net operating costs vary widely according to operating conditions, of course, and are estimated at $10.85 per ton to $5.55 per ton for the base comparison cases of 250 TPD to 2,000 TPD plants. On an incremental basis, the addition of a steam recovery package gives the whole system an operating cost reduction ranging from $0.18 per ton at 500 TPD, to $1.10 per ton at 2,000 TPD. This is not a large benefit and is, of course, derived only from the organic part of the waste that is incinerated for disposal at the steam value given in Table 3. Steam recovery operations face some rather special market limitations. While heat is a universally usable energy source, it is limited to very short transport distances. Thus, there must be a customer near the heat source with requirements suited to the particular incineration operation. In past years, steam recovery has often complicated operation of waste disposal operations, because waste burning and contract heat delivery requirements often get "out of phase." The new heat recovery techniques appear to be more technically manageable, but the limitations of the waste incinerator and steam customer interface are still severe. In addition, the value of steam varies widely. This approach to resource recovery gives an inflexible situation--steam is delivered as produced or lost; and it must be delivered in the contracted quantities requiring standby fuel for periods of low refuse heat value. It appears that heat recovery is an attractive method under very restricted conditions. From a practical standpoint, the market potential is quite restricted. By contrast, the economic and institutional barriers to steam recovery appear to be much less restrictive in foreign countries. 3.2.4 Incineration with steam generation and residue recovery. The various resource recovery components and subsystems can be combined in many different ways. One such logical combination is steam generation coupled with incinerator residue recovery. Here, the same comments apply as to the concept considered individually in the preceding sections. Tables 10 and 11 summarize the pertinent economic data for this combination of alternatives. As would be expected, the capital requirement of $11.7 million is higher than for either residue recovery or steam generation alone, and operating costs of $11.69/ton are substantially greater. However, the value of recovered resources, at $5.12 per ton, when credited against the annual operating costs, results in a net operating cost of just $6.57 per ton at the 1,000-TPD level. Since this net cost is significantly lower than for either steam generation or residue recovery by themselves, the addition of residue recovery capabilities appears to be economically attractive in situations where steam generation can be justified. |