Thermoeconomic analysis of cogenerated refuse energy recovery plant with thermal storage

This thesis develops thermoeconomic (second law and present worth) analysis and investigates the feasibility of employing thermal storage for cogenerated refuse energy recovery using mass-burning water-wall incinerators and topping steam turbines. A typical design is envisioned to be modular in nature so that it may be applied to various size loads without major engineering modifications. Each module is rated at 150 tpd of refuse capacity, 750 kW of electrical power, and 26,200 lbm/hr (11,900 kg/hr) of 150 psig (1140 kPa absolute) steam. As an option, condensing turbines are considered to receive unused process steam in the case of reduced steam load. The results indicate that this option is not economically feasible for a typical off-peak utility-purchase rate which leads to the idea of storing the excess energy during off-peak periods and recuperating it during peak periods. Sensible thermal storage is considered in rectangular cross-sectional channels through which is passed unused process steam during the storage period and feedwater during the recovery period. In determining the optimum storage configuration, it is found that the economic feasibility is a function of of mass and specific heat of the material and surface area of the channel as well as cost of material and fabrication. Economic considerations included typical cash flows of capital charges, steam and electrical energy revenues, refuse tipping fee, operation and maintenance costs, and income taxes. Cast concrete is determined to be a potentially attractive storage medium.