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At the present time, the sewage treatment plants in the United Kingdom produce about 25,000,000 t of sewage sludge each year at a concentration of 4% solids. New regulations in the United Kingdom forbid sea dumping, and in the near future new incinerators will be required to dispose of about 5,000,000 t per year. The research program at the Sheffield University consisted of design and construction of a small-scale cylindrical rotating fluidized bed incinerator with an inside diameter of 200 mm and an axial length of up to 200 mm. The fluidizing medium was silica sand (0.6-0.7 mm) and the bed depth 30-50 mm. The rotational speed of the bed varied between 100 and 1,000 rpm (which produced 1-100 g loading). Coal, oil, sewage sludge, and chicken manure (biomass) were burnt in the bed at temperatures between 700 [degrees] and 900 [degrees] C. Measurements of heat transfer rate, bed temperature, and exhaust gas composition were carried out over a range of operating conditions. The influence of rotational forces on basic fluidization characteristics (pressure drop, minimum fluidization, and particle mixing) were also investigated on a perspex model. The results obtained from the research work demonstrated that the rotating fluidized bed incinerator can produce considerably higher combustion intensities (i.e., process intensification), has a wide turn-down range (i.e., versatile), has low toxic emissions (i.e., clean technology), and has a more easy and rapid start-up than conventional stationary fluidized bed incinerators. Other advantages of the system include: good mixing, simpler fuel injection, low thermal inertia, and good heat transfer rates. Other potential applications for this system include boilers, open cycle gas turbines, and combined gas/steam cycles.

This paper discusses a number of design modifications and changes in operational conditions that have a major influence on the overall performance of the large Coventry municipal incinerator plant (65 MW), which incorporates a heat recovery system for district heating. Four different secondary air-injection systems and various primary air-distribution patterns along the grate were investigated using a computational fluid dynamic model, in an attempt to obtain optimum combustion conditions that would minimize potential emissions of toxic pollutants and reduce maintenance costs at the plant. The modeling work showed that the use of four large high-speed secondary air jets firing toward a common center, together with optimizing the primary air distribution along the grate, produces substantially longer residence times and improves temperature profile at the exit. The novel feature of the proposed secondary air-injection system is the formation of a large and significantly strong recirculation zone, located above the burning refuse bed, in the middle of the furnace shaft. This strong recirculation zone improves the overall performance of the incinerator due to intensive mixing of hot gaseous products evolving from the refuse bed with the combustion air supplied as the secondary air, and greatly improves the gas phase combustion and helps to reduce emissions of chlorinated organic compounds. Results obtained clearly demonstrate that the proposed secondary air-injection system has an excellent potential to satisfy most requirements for emissions levels and gas resident times specified by the European Directives (EEC) for municipal incinerators with a vertical radiation shaft.

The transient process in a full-scale municipal solid waste incinerator was investigated to assess the effect of the grate movement and waste feeding cycles. Inside-bed measurements of temperature and O2 were carried out and an 18-hour record of furnace temperature, airflow, and flue gas compositions was analyzed using discrete Fourier transform. The transient burning process was also simulated numerically by solving the governing equations for both the solid and gas phases. It is found that fluctuations in the furnace temperature and flue gas O2 level correspond to the waste feeding and grate movement cycles, either in phase or out of phase (depending on the length of the cycles), while combustion inside the bed is dominated by a series of big spikes and dips in both local temperature and O2 level. Theoretical calculations indicate that each grate movement causes a surge (by 35%) in the volatile release rate but a depression (by 24%) in the char burning rate. The overall bed-burning rate fluctuates between 90 and 110% of its average. [ABSTRACT FROM AUTHOR]

Presents a study measuring the gas-residence time in large incinerators using the pseudo-random binary sequence stimulus tracer response technique at the Sheffield, England municipal solid-waste incinerator. Determination from the carbon dioxide concentration in flue gases at the boiler exit; Comparison of data calculated by computational fluid dynamics.

Describes a finite-difference mathematical model for the prediction of the three-dimensional reacting flows within a garbage incinerator. Focus on the influence of the design and operating parameters on the overall performance of the incinerator; Recommendations for design improvements.

The main purpose of this research was to investigate the possibility of incineration of wool scouring sludges in a novel vertical axis rotating fluidized bed (RFB). A small-scale RFB was designed and constructed with an internal diameter (ID) of 200 mm and height of 50 mm to carry out the experiments. In phase one of the experiments, a cold test was conducted to investigate the fluidization performance of the RFB, which eventually led to the optimisation of the operating parameters, i.e., sand particle size, rotation speed and bed loading (bed thickness) which ensures complete fluidization and minimum particle elutriation. Sand particle size of 0.5 to 0.6 mm, rotation speed of 200 to 400 rpm and bed loading of 1 kg (equivalent to bed thickness of 27 mm) were found optimal. These information generated were useful for the second phase of the experiments, which was the hot test, in investigating the possibility of incinerating wool scouring sludges in the RFB. Nine wool sludges from different process routes generated from the wool scouring industries were analysed for their compositions. Most of these sludges were highly moist, had high volatile matter and high ash content with low level of fixed carbon. These characteristics made incineration difficult. Hence, the effect of varying the moisture content, rotation speed and sludge feed rate on the incineration of the three selected sludges were studied in the hot test. With 5% support methane, all sludges with a maximum moisture up to 70% as-received could be successfully burned in the RFB at rotating speeds of 200 and 300 rpm. The combustion was found to be intense with a high efficiency due to the good turbulence and mixing in the RFB. The combustion gases produced, i.e., CO, CO(2) and NO(x) were reasonably low due to the high combustion intensity and efficiency. To study the dynamics of the bed and freeboard region in the RFB, the velocity flow field was simulated using a computational fluid dynamics (CFD) model to generate information of the flow pattern. The special advantages of swirling flow would benefit the gas combustion in the RFB. The experimental results obtained have suggested that the incineration was successful and the ash particles elutriated were fine due to the good mixing and turbulence in the RFB. This also reflects the RFB as an effective incinerator.