Bio-SNG - CNG Services

BIO-SNG FEASIBILITY STUDY – ESTABLISHMENT OF A REGIONAL PROJECTA key design consideration therefore is whether to import material of a defined specification and quality orto manufacture the fuel on site from raw biomass or residues. On the one hand manufacture on site willdemand more space, more plant, a larger workforce and a significant parasitic energy consumption,however on the other hand, bought-in ready to use fuel will be more costly, and could subject the plant togreater supply chain vulnerability. Moreover biomass drying is likely to be a significant feature of the fuelpreparation process and could represent an economically effective use of waste heat from the gasificationprocess. A balanced judgement needs to be taken, therefore, on the fuel supply philosophy, taking intoaccount, the type of raw feedstock (lumber, waste wood, wood chip, pellets, miscellaneous biomassresidues, commercial / industrial waste etc.), the plant location, the space available, and the fuel supplychain arrangements.There is extensive expertise in the area of fuel reception, preparation and handling, however, it is acommon location for serious process malfunctions; due diligence experience reveals a consistent andrecurrent problem with fuel preparation, quality and feeding. It is vital, therefore at the design stage touse proven and reliable designers, and equipment suppliers and to confirm that the process plant willoperate with the particular material specifications envisaged for fuelling the gasifier. Solids handlingsystems must be designed in consideration of the particular properties of the materials in question; forexample it would be unwise to assume that woodchip will behave in a handling system in the same wayas wood pellets. CEN/335 goes some way to describing standard test methods that can be employed todetermine the critical handling attributes of particular solid biomass fuels.5.2 GASIFICATIONThere are fundamentally three main types of gasifier:Fixed bed (down-draft and up-draft)Entrained flowFluidised bed (direct and indirect heating)Fixed bed biomass gasifiers are used extensively in some parts of the world in small, relatively crudeapplications producing a low quality gas for small scale power generation. Fixed bed gasifiers are alsoused at a large scale, however, the low carbon intensity of biomass fuels makes them unsuitable for usein large scale fixed bed gasifiers, unless they are co-fired with coal. On this account it is proposed thatfixed bed gasifiers should be excluded from further consideration where the intent is to produce biosyngasat a moderate industrial scale.33