Abstract
Material feeding and handling systems have been cited as one of the most common causes of process downtime where thermochemical conversion processes are concerned. New and emerging fuels come in a variety of forms, and if such fuels are to be deployed widely it is imperative that material feeding and handling systems are designed appropriately. This study proposes an approach for designing material feeding and handling systems for use with coarse solid fuels. The data obtained from this study indicates particle size to be one of the key issues affecting the flowability of bulk solids further to the uniformity in particle shape. Coarse bulk solid samples were shown to flow more freely than their milled and pulverised counterparts, generating higher degrees of flowability. The results from this study were also applied to a new feed system used for feeding solid fuels to high pressure processes named the Hydraulic Lock Hopper. In this study the Hydraulic Lock Hopper demonstrated the feeding of wood pellets, torrefied spruce pellets, and ground anthracite coal grains against a pressure of 25 barg in two modes of operation. Energy savings compared to conventional lock hopper systems were recorded in the region of 80%.
Highlights
The number of biomass fed systems has increased dramatically in recent years and with this much has been learnt about the dynamics of operating a biomass fired plant
The Jenike design procedure was explored for a broad range of materials with varying particle size and shape for use in new high pressure solids feed system, the Hydraulic Lock Hopper
Large scale shear testing equipment was used to quantify the interparticle friction effects of four coarse fuels: wood pellets, torrefied wood pellets, torrefied wood chips, and ground anthracite grains, and the Brookfield Powder Flow Tester was used in conjunction with two fine fuels: milled wood pellets and pulverised bituminous coal
Summary
The number of biomass fed systems has increased dramatically in recent years and with this much has been learnt about the dynamics of operating a biomass fired plant. Due to the apparent similarities to coal plants, many mistakes have been made in the development and utilisation of biomass fuels in thermochemical conversion processes, not least where material handling and feeding are concerned [1, 2]. Where combustion and gasification systems are concerned, material feeding and handling systems have been cited as one of the most common causes of process downtime, especially when handling new and emerging fuels [3, 4]. Problems have arisen due to inadequately designed and sized equipment and where biomass species have been assumed to behave in a convenient and stable manner like their coal counterparts. Biomass species behave far differently to coals and generally have a greater risk attached with them when they are handled due to their higher reactivity [5, 6]. Wood dust ignites at much lower temperatures than coal dust and requires a significantly lower amount of energy for ignition [7]
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