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1974-National-Incinerator-Conference-18



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A Chronology of the Nashville Tennessee Incinerator with Heat Recovery and the Compatible Central Heating and Cooling Facility MAURICE J WILSON I C Thomasson Associates 1 nco Nashville Tennessee The so called energy crisis is not a crisis of fuel deple tion as much as a crisis of rapidly rising costs The crisis in energy follows our life style It is not the high cost of living it is the cost of high living We have misused some of our fossil fuels during the past 100 years with the result that certain nonrenewable resources will be exhausted in the next few decades How ever since we are beginning to face the situation realisti cally it is to be hoped that new sources of energy may be found and that instead of a decline in our conveniences we may continue to enjoy increasingly high living stan dards Conceivably by the year 2 000 we may have learned how to tame the sun s energy and to perfect hydrogen fusion Already we have learned that solid waste may be con verted into a useful commodity that it may be an asset instead of a liability that we may get cash for trash A thermal plant to achieve this very goal is nearing com pletion in Nashville Tennessee Solid waste is being generated at an ever increasing rate The heat energy in the replaceable resources component of our solid waste increases each year Projections for 1975 indicate the daily per capita disposal rate for resi dential and commercial wastes will be approximately 5 5 pounds and the heat content 4 650 Btu s per pound an increasing source of heat energy The Nashville project was originally conceived in 1969 as a fossil fuel fired central heating and cooling plant the construction of which would be interfaced with the Urban Renewal Program of The Nashville Housing Authority The facility would serve in the central business district the metropolitan government office buildings state office buildings and privately owned buildings such as com mercial offices stores banks motels and hotels Central plants can produce the coolant and heat at a lower cost than the decentralized approach Capital costs in new buildings can be reduced and less atmospheric pollution results when the heating and cooling services are provided by a single plant The initial feasibility study authorized by the city indicated Significant owning and operating cost advantages to the city state and private clients Municipal officials responsible for the economics and disposal problems of solid waste were confronted with many new state and federal standards immediately follow ing the submission of the initial comprehensive feasibility study A supplementary study was initiated with the objective of using the heat energy in the city s solid waste in lieu of fossil fuels The steam would serve the in plant requirements as well as year round heating and cooling needs of the 27 buildings which had already contracted for the commodities The Nashville Thermal Transfer Corporation was chartered under the laws of Tennessee in May 1970 This not for profit tax exempt corporation was authorized to issue tax exempt revenue bonds construct own and operate the solid waste incineration facility and distri bution system in downtown Nashville until such time as the bonded indebtedness was satisfied after which the assets would become the property of the metropolitan government The NITC was fmanced solely through the issuance of revenue bonds backed by the system s 30 year user con tracts It was imperative therefore that a sufficient 213 number of customers be signed to guarantee full amorti zation of the bonds In other words the contracts for sale of the heat energy in the form of coolant and steam were consummated before the bonds were offered for sale The plant size was established by the commodity demand and construction then authorized The Phase I bond issue was 16 500 000 About 12 800 000 was for plant and distribution system Site acquisition was 300 000 legal financing and design fees about 1 000 000 interest during construction about 2 000 000 capitalized debt service approximately 1 000 000 Earned interest during construction was about 600 000 First year operating revenue plus other income from the city for incineration of the waste instead of landfill exceed operating expenses and debt service by about 250 000 Projected growth in number of clients served increase in plant capacity increase in revenues and some increase in operating expense will produce a net balance available after debt service of well above the quarter million dollars The NTTC user contracts provide that with the addi tion of new customers to the system and a correspondin decrease in the cost of production savings will be passed on in the form of rebates to the clients thus effectively reducing the cost of heating and cooling the buildings served by NTTC These easily demonstrable savings made the task of selling the idea to prospective clients consider ably easier The distribution systems serving downtown Nashville are shown on Fig 1 The main coolant headers are 42 in diameter direct burial uninsulated the steam supply 20 in diameter insulated and the condensate return 10 in diameter uninsulated The header system is sized for the ultimate flow Coolant is supplied at 41 F with 57 F return at design Steam supply is 150 pounds satur ated with condensate return at atmospheric pressure This sequence of detellllining the market needs then building a plant of compatible size seems a logical ap proach Solid waste sufficient to meet NTTC fuel needs will be delivered at no cost pursuant to the terms of a 30 year agreement between the city and the corporation The contract also stipulates that title to the solid waste during the incineration or volume reduction process remains with the city and that any financial return from recycling of the material would benefit the city In the event that normal solid waste delivery be inter rupted by a strike of the sanitary workers or incineration be disrupted by major repairs a standby package steam generator using the spent oil has been incorporated in the plant It is imperative that dependable service to the clients be provided throughout the year For Phase I this is a more economical method for providing standby than an additional incinerator unit Initial plant capacity is 720 daily tons of solid waste with production capacity of 13 500 tons of coolant and 218 000 pounds of steam per hour The ultimate is 32 750 tons of coolant and 460 000 pounds of steam per hour produced


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