| Gasification of sludge is carried out on sewage | | | | comparison with direct combustion units. Waste |
| sludges with energy production or pyrolysis of the | | | | fuel gasification generally involves heating fuel in an |
| thermally dried residues, under a non-oxidizing | | | | oxygen-starved environment to produce a |
| atmosphere. It can be a means of alternative | | | | medium or low calorific gas. |
| renewalble fuel production and it could in part be a | | | | Gasification of sewage sludge for heat and power |
| solution to the environmental problems that | | | | generation in combined heat and power (CHP) |
| landfilling or conventional combustion could create. | | | | applications is an attractive concept that provides |
| The present work which also focuses on | | | | an environmentally acceptable, efficient, and |
| combustion and pyrolysis of cotton gin residues in | | | | economically viable means of generating energy |
| Greece, is another example of alternative ways | | | | from a waste disposal problem. The final solid |
| of energy production. All these methods are using | | | | residues are pathogen-free but may contain toxic |
| biomass as an energy source, and the use of this | | | | elements such as barium, copper, mercury, lead, |
| as an energy source is expected to grow rapidly. | | | | and zinc at levels that could make their disposal to |
| Recently, gasifier operation has been put on a | | | | landfills costly as well as environmentally |
| sound thermodynamic footing by a number of | | | | questionnable. |
| technology provider companies. It has been | | | | However, these materials would also be produced |
| shown that, apart from its deleterious impact on | | | | by incineration, and gasification makes the overall |
| thermal efficiency, the presence of water in | | | | sustainable benfits so much more positive when |
| mechanically-dewatered fuel (containing ~ 32 wt% | | | | the usefulness of gasification syngas is considered. |
| solids) does not lead to significant particle break-up | | | | Fuel gases from gasifires can be cleaned and then |
| compared with dried fuel. | | | | burned in internal combustion engines for the |
| Gasification has been demonstrated using partial | | | | generation of electricity and process heat, or |
| oxidation in three stages before final combustion. | | | | stored and used as feedstock for other chemical |
| When doing this it has been shown that the NOx | | | | production. |
| was reduced from several thousand ppm to | | | | Wastes can even be co-processed with coal to |
| around 25 ppm. This is a truly significant reduction | | | | yield gas and liquid fuels or chemical feedstocks. |
| in favour of gasification. | | | | Specific approaches discussed include: gasification |
| Gasification in fluidized bed reactors and usually | | | | of sewage sludge, straw, wood wastes, and |
| takes place in a fluidized bed formed above the | | | | plastics; liquefaction of paper and plastic wastes, |
| slag bath and constituted by the dried sewage | | | | papermaking wastes, oils, greases, waste tyres |
| sludge or waste materials, the solid fuel, the | | | | and waste-derived liquids; pyrolysis of plastics; and |
| oxygen-containing gas and the gasification gas. | | | | economic studies. |
| The gas produced in the gasifier can be used for | | | | Wastes selected included dewatered sewage |
| power generation or as a reducing gas for iron | | | | sludges, loaded rotary hearth furnace cokes, and |
| ore, or any one of a large selection of uses. | | | | processed packaging plastics. A number of plant |
| Gasifiers can frequently handle high fouling fuels | | | | modifications may need to be made to |
| without excessive slagging/fouling due to the | | | | accommodate these feedstocks. |
| lower temperatures at which they can operate in | | | | |