Waste Management

Abstract

The present invention relates to a method for producing steam, the method comprising: (a) passing waste gas through a first boiler to produce steam having a first temperature, and cooled waste gas; (b) removing contaminants from the cooled waste gas to produce clean waste gas; (c) passing the steam having a first temperature through a second boiler; and (d) burning at least a portion of the clean waste gas in the second boiler to produce steam having a second temperature, the second temperature being higher than the first temperature. The method is particularly suited to efficiently generating high temperature, high pressure steam derived from the pyrolysis/gasification of organic waste.

Claims

1-28. (canceled)

29. A method for producing steam, the method comprising: (a) passing waste gas through a first boiler to produce steam having a first temperature, and cooled waste gas; (b) removing contaminants from the cooled waste gas to produce clean waste gas; (c) passing the steam having a first temperature through a second boiler; and (d) burning at least a portion of the clean waste gas in the second boiler to produce steam having a second temperature, the second temperature being higher than the first temperature.

30. The method of claim 29, further comprising an initial step of gasifying waste organic material to produce waste gas.

31. The method of claim 29, wherein the waste gas used in step (a) has a temperature of at least 400 C.

32. The method of claim 29, additionally comprising monitoring the first temperature and/or the pressure of the steam obtained in step (a).

33. The method of claim 32, further comprising controlling the first temperature and/or pressure of the steam obtained in step (a).

34. The method of claim 29, wherein the steam has a first temperature of no more than 400 C.

35. The method of claim 29, wherein the steam produced in step (a) has a pressure of at least 40 bar.

36. The method of claim 29, wherein the second temperature is at least 450 C.

37. The method of claim 29, comprising burning a first portion of clean waste gas in the second boiler and supplying a second portion of clean waste gas to power generation equipment, such as an internal combustion engine or a gas turbine, for the direct production of electricity.

38. The method of claim 37, further comprising adjusting the ratio of the first portion of clean waste gas supplied to the second boiler to the second portion of clean waste gas supplied to the power generation equipment.

39. The method of claim 37, additionally comprising passing exhaust gases from the power generation equipment through a third boiler, thereby obtaining a second batch of steam and cooled exhaust gases.

40. The method of claim 39, further comprising passing the second batch of steam through the second boiler.

41. The method of claim 39, comprising passing the cooled exhaust gases produced by the third boiler to the second boiler where they are burned.

42. The method of claim 29, further comprising using the steam obtained in step (d) to drive a turbine to generate electricity.

43. A waste-to-energy system comprising: a reactor for gasifying organic waste to produce waste gas; a first boiler comprising a gas inlet, a water inlet, a gas outlet, and a steam outlet; a cleaning apparatus; a second boiler comprising a gas inlet, a gas outlet, a steam inlet and a steam outlet; and a steam turbine comprising a steam inlet, wherein a flow path for gas is provided from the reactor to the second boiler via the first boiler and the cleaning apparatus, and a first flow path for steam is provided from the first boiler to the steam turbine via the second boiler.

44. The system of claim 43, wherein the cleaning apparatus comprises a gas inlet, which is fed by the gas outlet of the first boiler, and a gas outlet.

45. The system of claim 43, wherein the gas inlet of the second boiler is connected to the gas outlet of the cleaning apparatus and the steam inlet is connected to the steam outlet of the first boiler.

46. The system of claim 43, wherein the gas flow path is branched at or just after the cleaning apparatus, wherein a first branch is provided between the cleaning apparatus and the second boiler, and a second branch is provided between the cleaning apparatus and a power generation unit.

47. The system of claim 46, wherein the power generation unit comprises a gas inlet and a gas outlet, the gas inlet being connected to the gas outlet of the cleaning apparatus.

48. The system of claim 46, further comprising a controller for controlling the distribution of gas between the first and second branches.

49. The system of claim 48, wherein the controller comprises a valve positioned at the point at which the first flow path branches.

50. The system of claim 48, additionally comprising a control unit which is operatively linked to the controller whereby to automatically adjust the distribution of gas flow between the first and second branches.

51. The system of claim 46, wherein the second branch is provided from the cleaning apparatus to the second boiler, via the power generation unit.

52. The system of claim 51, wherein the second branch additionally passes through a third boiler positioned between the power generation unit and the second boiler.

53. The system of claim 52, wherein a second flow path for steam connects the third boiler to the first steam flow path upstream of the second boiler.

54. The system of claim 43, additionally comprising one or more sensors for monitoring the temperature and/or the pressure of the steam and/or other gases.

55. The system of claim 54, further comprising one or more controllers for controlling the temperature and/or the pressure of the steam, the waste and/or exhaust gases, and/or the water supply.

56. The system of claim 55, wherein the controllers are configured to automatically adjust the temperature and/or the pressure of some or all of the fluids to be within predetermined limits in response to information received from the sensors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0064] Embodiments of the invention will now be described with reference to the accompanying Figure in which is a schematic diagram of a waste gas management system in accordance with an embodiment of the present invention.

[0065] With reference to FIG. 1, a waste gas management system 10 comprises a gasification or pyrolysis unit 12, a first heat recovery boiler 14, a second boiler 16, a cleaning apparatus 18, and a steam turbine 20. The system 10 additionally comprises a power generation plant 22 and a third boiler 24, all being connected by conduits defining the various flowpaths.

[0066] A first flow path A for the transfer of gas is provided from the gasification unit 12, through the first boiler 14 and on to the cleaning apparatus 18. At this point the flow path A branches into a first branch A1, which leads directly to the second boiler 16, and a second branch A2 which leads to the second boiler 16 via the power generation plant 22 and the third boiler 24. A computer controlled valve 26 is positioned at the point of divergence between the first and second branches A1, A2.

[0067] A second flow path B for the transfer of steam is provided from the first boiler 14 to the steam turbine 20, via the second boiler 16. The second flow path B is fed by a further flow path C, which is supplied by the third boiler 24.

[0068] In use, waste gas (syngas) produced by the gasification unit 12 travels along the first flow path A to the first boiler 14, where heat is recovered from the waste gas to produce a first flow of high pressure, low temperature steam and cooled waste gas. The first flow of steam exits the first boiler 14 via a steam outlet and is transferred to the second boiler 16 via a pipe 28.

[0069] The cooled syngas is transferred from the first heat recovery boiler 14 via a pipe 30 to the cleaning apparatus 18, in which contaminants are removed from the syngas.

[0070] A first portion of the clean syngas is supplied by a pipe 32 (along flow path A2) to a power generation plant 22. The power generation plant 22 may be, for example, an internal combustion engine, or a gas turbine, which converts the clean syngas directly into electricity. Exhaust gases released from the power generation plant 22 are directed via a pipe 34 to a third boiler 24. The third boiler 24 recovers heat from the exhaust gases to produce a second flow of steam, which is supplied through a conduit 36 (along flowpath C) and combined with the first flow of steam before being passed into the second heat recovery boiler 16. Cooled exhaust gases released by the third boiler 24 are also supplied via a pipe 38 to the second heat recovery boiler 16 for burning.

[0071] A second portion of the clean syngas produced by the cleaning apparatus 18 is directed via a pipe 40 to the second heat recovery boiler 16 (along flowpath A1), where it is burned together with the cooled exhaust gases from the third boiler 24. The energy released is used to heat the combined first and second flows of steam supplied by the first and third boilers 14, 16. The second heat recovery boiler 16 releases high temperature, high pressure steam which is supplied via a pipe 42 to a steam turbine 20 for generating electricity. Flue gases from the second and third boilers 16, 24 are diverted to a stack.

[0072] The computer controlled valve 26 is adjusted to vary the proportion of gas passing along flowpaths A1 and A2. In this way, the proportion of syngas being combusted to generate electricity directly in the power generation plant can be balanced against the use of syngas to generate electricity indirectly through the steam turbine 20. It has been found that by managing the syngas according to the method and system of the invention, energy recovery is maximized to achieve an efficiency of 32-33%, as compared to just 27% for conventional energy recovery systems.