Development of a fluidized-bed coal pretreatment system for coupling to a fluidized-bed boiler

摘要

The Energy & Environmental Research Center (EERC) has developed and patented a system that upgrads the quality of lignitic and subbituminous coals by taking advantage of several of the unique properties of these coals. This fluidized-bed system, identified as the Controlled Spontaneous Reactor (CSR), uses a unique distributor plate design to impart a variable velocity across the bed to effectively size-segregate the treated coal. The CSR can use low-temperature (300 deg F) stack gas as its primary heat source to serve a variety of facilities as a primary fuel conditioner. Controlled combustion of a small portion of the coal within the CSR provides any heat required for treating the coal. The specific application addressed in this paper is the ability of the CSR to enhance fuel flexibility, increase capacity, improve turnown performance, and reduce NO_x and N_2O emissions when coupled to a fluidized-bed combustion boiler. Pilot plant data used to develop and prove the system will be presented. The general advantages of the CSR are its high specific throughput, simplicity of operation and control, and adaptability to a wide range of feedstock particle sizes (up to 3-inch top size). The CSR has the inherent ability to control the properties of the product, including physical size, moisture, volatile matter, and heat content simply by selecting the appropriate combination of design and operating parameters. Its relatively small size and simplicity should minimize the cost of installation in a new or existing plant.