FIELD OF INVENTION:
This invention generally relates to a fluidised bed coal gasification reactor for effective gasification or combustion of coal or carbonaceous particles. More particularly, the invention relates to an improved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant
BACKGROUND OF THE INVENTION
Fluidised bed reactors are used to gasify coal for power generation, production of chemicals combustion and steam generation. Typically they consist of a reactor chamber and a lower distributor plate for supporting a bed of particulate materials which usually comprise carbonaceous or fuel material, inert bed material such as coal ash and adsorbents for removal of Sex The distributor plate has typically a plurality of nozzles or openings to allow passage of the fluidising/reacting gaseous media into the reactor. A wind box or air plenum is disposed below the grid plate and gas or air is introduced into the reactor above which keeps the bed above in a suspended state. A compressor or blower is used to deliver gases into the plenum chamber at the required pressure. The gas flows upwardly into the fluidised bed reactor through the nozzles located on the distributor plate and enables the particulates in the bed to be suspended in a stream of air or gases. As a result of this suspension of particulates in the fluidising media good mixing of the particulates and gases is achieved in me reaction chamber. This results in essentially uniform temperatures over the height of the fluidised bed resulting in effective gasification or combustion of the coal or carbonaceous particles with good heat and mass transfer characteristics.
Pressurised Fluidised Bed Coal Gasification Reactor is a preferred means to convert coal into fuel gases for burning in a gas turbine combustor to generate electric power. The process is especially suited for conversion of high ash coals, such as Indian coals containing mineral matter in the range of 30 to 40%. The thermal energy in the exhaust of the gas turbine is utilised in a bottoming cycle, for example a Rankine cycle, to generate
additional electric power. There are several configurations utilising a gas turbine or a fuel ceil which depend on the fluidised bed coal gasifier to provide the fuel gases for power generation. Capacities required of the pressurised fluidised bed coal gasification reactors has to be high for power generation applications. Increase in capacities of fluidised bed coal gasifiers are obtained either by increasing the pressure of operation of the gasifier or by an increase in the diameter of the fluidised bed zone in the coal gasification reactor. However the maximum pressure for which the gasifier can be designed to maximise the cycle efficiency is mainly dependent on the fuel gm entry specifications of the gas turbine. And operating the gasifier beyond mis maximum pressure will be detrimental to overall cycle efficiency. After the optimum gasifier pressure is determined based on gas turbine requirements the only way to increase the capacity of a single gasifier is to increase the gasifier diameter. It is well appreciated and accepted that increase in diameter of a fluidised bed gasifier has limitations and requires extensive testing because of changes in the hydrodynamic behavior with reactor diameter, which affects coal conversion. Attempts to scale up from pilot sized gasifiers (400-5 00mm ID) to sizes larger man 2m ID have resulted in several failures. On the other hand recourse to a number of smaller gasifiers to meet the fuel gas requirements will be detrimental to the overall economics of the power plant, in addition to the cost and complexity of increasing the number of downstream gas treatment and heat recovery streams.. The present invention provides a means to increase the capacity of a fluidised bed coal gasifier, by providing atleast of two fluidised bed reactors inside a single pressure housing, such mat the diameter of the reactor bed is kept within safe limits from hydrodynamics point of view, established by testing or within experimentally validated zone of hydrodynamics of the process. Such a configuration has the added advantage of having a single stream of cyclone separators and heat recovery boiler as opposed to having multiple units having the same reactor diameter for me fluidized bed coal gasifier.
OBJECTS OF INVENTION.
It is an object of this invention to propose an improved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant, which provides higher per-unit conversion capacity.
A further object of the invention is to propose an improved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant, which limits the diameter of the flmdising zone of the reactor to values within the ranges of hydrodynamic scalability as established by experimental testing or analytical methods.
It is still further an object of this invention to propose an unproved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant, which reduces the number of independent fluidised bed gasifier units to cater for the requirements of, for example a gas turbine, in a coal based combined cycle power plant
It is another object of this invention to propose an improved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant, which minimizes the number of heat recovery and dust removal streams required to meet the load requirements of a gas turbine in a coal based combined cycle plant.
It is yet another object of mis invention to propose an improved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant, which reduces the numbers of coal feeders and ash removal equipment per unit of gasifier throughput, thereby effecting reduction in installed cost of the plant
It is yet a further object of this invention to propose an improved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant,
which be configured with atleast two fluidised bed reactor zones within a common pressure housing, to fetch the attendant benefits of cost reduction, smaller overall plant area requirement as opposed to the prior art reactors.
It is still another object of this invention to propose an improved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant, in which suitable material transfer port be provided between the two reactor beds housed inside a common pressure housing, to enhance uniformity in process conditions such as reactor bed temperatures and gas compositions in me congniently disposed fluidised bed zones, which in turn improve the performance of the gasifier.
It is also an object of this invention to propose an unproved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant, in which independent plenums be designed for introducing the fluidising media into the two fluidised bed zones, so that it is made possible to start bed ignition and startup of one of the beds initially, and subsequently build up the bed in the other fluidised bed by enabling transfer of hot bed material from the first bed into the other through specially provided transfer ports or openings in the common metal supported refractory lined reactor wall between the two beds. This is achieved after initial ignition and start up of the bed in a static mode and subsequent increase in height of the expanded bed by constant fuel addition in the first bed and causing hot bed material to move into the adjacent bed through ports provided for the same, till such time that bom beds build up to the same bed height, whereupon fuel and fluidising media are introduced into the othelr bed also and the two start operating in unison at the same bed height
It is also a further object of this invention to propose an unproved pressurized fluidized bed, gasification reactor adaptable, in particular in a coal based combined cycle power plant, which has atleast two independent plenums for the two fluidised bed reactors housed inside a common pressure housing, to achieve better distribution of the fluidising media across the individual fluidised bed zones, to improve the process efficiency, by improved gas-particle contact
It is again an object of this invention to propose an improved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant, which be provided with openings in the common wall separating the two fluidizing bed reactors at a height from the bottom of the gasified of approximately one diameter of the fluidised bed reactor, whereby initial heating and start up of fluidized bed can be done by starting only one of the beds and subsequently transferring the hot bed material from the first one into the other after the first bed is fluidized and constant coal feed is initiated. This provision is planned to minimize startup energy requirements in addition to other benefits detailed above.
It is yet again an object of this invention to propose an improved pressurized fluidized bed gasification reactor adaptable, in particular in a coal based combined cycle power plant, in which the independent plenums for the two fluidized bed zones, in combination with the material transfer ports or opening reduces the bubble growth in the axial direction of the fluidized bed, because of pressure perturbations caused by transfer of material across the transfer ports.
An improved pressurized fluidized bed gasifier adaptable, in particular in a coal based combined cycle power plant, comprising :
- means for entry of coal into the gasifier;
- means for entry of fluidizing media into the gasifier;
means for ash removal disposed at the bottom of the gasifier being flowably connected at one end with the reactor zone, the other end leading to a bottom ash discharge port;
characterized in that the fluidized bed reactor zone of the gasifier is configured as at least two separate reaction zones having identical internal diameter to correspond together the diameter of the un-separated reactor zone, in that the two separate reaction zones having a common freeboard region with separate gas plenums including ash removal pipes, and in that a separating member is disposed between the at least two separate reaction zones having a transfer port so as to maintain a continuous inter-transfer of bed material and gaseous reactants between the at least two separate reactor zones.
The invention will be better understood in the following description according to the accompanying drawings In a non restrictive manner wherein
Fig. 1 indicates the major equipment and sub systems which constitute an Integrated Gasification Combined Cycle Plant, wherein the present invention is intended to be employed.
Fig. 2 shows the configuration of a Pressurised Fluidised Bed Coal Gasifier having an internal diameter in the fluidizing zone of W2d'.
Fig. 3 shows the present invention which substitutes two fluidized bed zones of internal diameter 'd' in place of a single fluidized zone of internal diameter W2d', inside a common pressure housing.
Fig. 1 shows a schematic layout of an Integrated Gasification Combined Cycle Plant based on a Pressurised Fluidised Bed Coal Gasifier (1), indicating the present art Several variations of the scheme are possible which is centered on the Pressurised Fluidised Bed Goal Gasifier (1). The Pressurised Fluidised Bed Coal Gasifier (1) typically has provision for entry of coal (2) into the gasifier (1), provision at the bottom tor ash removal (3), provisions for entry of fluidising/gasifying media (4), provision for gas exit etc. The foal gas stream exiting the gasifier at temperatures of approximately, 1000 deg. C is typically routed through a series of dust separation devices (eg: cyclone separators) followed by heat recovery equipment where me fuel gas temperature is brought down to approximately 125 to 150 deg C, to enable use of pressure and flow control elements which cannot be reliably designed or operated at the temperatures prevalent at the gasifier outlet, before further gas cleaning and conditioning steps to achieve gas turbine specifications for fuel gas admission into me turbine combustor.
Fig 2 shows a vertical cross sectional drawing of a Pressurised Fluidised Bed Gasifier for coal, which is intended to convert coal or other carbonaceous materials in the solid state into fuel gases. The fluidised bed zone is configured as a single reactor without partition or separator, which is the existing practice or art The gasifier has a fluidised bed reactor zone (5) of internal diameter in the fluidising zone of 'V2 d\ a free board zone (6), a distributor (7) for introducing the fluidising reaction media into the reactor disposed above, located in the plenum (8), provision for coal entry (9) and fluidising media entry (10). A nozzle for fuel gas outlet (11) is provided near the top of the reactor. The fluidised bed reactor is lined internally with refractory and insulation material (12).
Fig. 3 shows the arrangement of the present invention intended to be the equivalent of the reactor described in fig. 2 and consists of two fluidised bed reactor zones of internal diameter 'd\ the two distinct fluidised bed reactor zones together have a cross sectional area equivalent to that provided in the fluidised bed reactor zone (5) referred above with
an internal diameter in the fluidising zone of'V2 d' me two fluidised bed reactor zones (13) have a common freedboard region (14) and gas outlet connection (15). The two fluidiaed bed reactor zones are provided with separate fluidising gas plenums (16) for entry of the fluidising media such as air and steam and ash removal pipes (17). The ash and agglomerates discharged from the two reactors are combined into one stream before exiting the gasifier through an opening (IS) provided for bottom ash discharge. The two fluid bed reactors share a common freeboard region (14) where the bigger particles disengage and fall back into the fluidised bed region (13) and the gases along with fine particulate materials leave the gasifier through a single exit (15) provided at the top. A metallic supporting and separating member (19) is provided to separate the two fluidising reaction zones. Transfer ports or opening (20) are provided on mis separating member to provide inter communication of bed material and gaseous reactants and products between the two fluidising reaction zones.
Examples/Preferred Embodiments:
The preferred embodiment is as shown in fig. 3 Two separate fluidised bed reaction regions (13) of internal diameter *d* are provided inside a common pressure housing with independent fluidising gas plenum (16) for introducing the fluidising media into the fluidising reaction zones. The gasifier is provided with required numbers of coal inlet provision (21). However the two fluidised bed reactors share a common freedboard, gas exit provision and bottom ash removal provision. The ash and agglomerates exiting the respective reaction zones enter the plenum by means of individual pipe connections, before they combine into one stream to exit the gasifier through the bottom ash opening (18).
The preferred embodiment provides two distinct fluidising reactor zones inside a common gasifier pressure housing. The diameter of the individual fluidising reactor zones are chosen in such a manner as to minimize scale up uncertainties as a consequence of choosing a larger diameter single fluidised bed, especially on account of uncertain or unknown bed hydrodynamics. As an example if the required diameter for a coal gasifier with a single bed to meet fuel gas requirements is '^2 d* the same can be met with the
preferred embodiment having two distinct fluidising zones each of diameter *d\ when the hydrodynamics are well established at the diameter 'dThe preferred embodiment retains many of the advantages of having a single larger diameter gasifier, such as, a common ash extraction system after the two ash streams from the two fluidised bed zones are combined into one, ahead of the bottom ash opening as described above, a common gas exit connection, a common freeboard region ahead of the fuel gas exit nozzle etc. The advantage of a single stream from the fuel gas exit nozzle connecting to dust separation devices and heat recovery devices are maintained, just the same as in the case of a gasifier having a single fluidising zone.
The preferred embodiment provides for interconnection of the two fluidising bed zones as described above for the purposes of faster startup, reduction of startup energy requirements. The interconnecting ports further improve me fluidising characteristics of the beds by breaking bubbles formed in the fluidising zone above the distributor plate because of small pressure fluctuations and differences caused in the two fluidising zones due to material exchange between the two fluidised bed zones.
The scope of the invention as narrated herein is defined in the appended claims.
WE CLAIM
1. An improved pressurized fluidized bed gasifier adaptable, in particular in a coal based combined cycle power plant, comprising :
- means for entry of coal into the gasifier (1);
- means for entry of fluidizing media into the gasifier (1);
- means for ash removal disposed at the bottom of the gasifier (1) being flowably connected at one end with the reactor zone, the other end leading to a bottom ash discharge port;
characterized in that the fluidized bed reactor zone of the gassifier (1) is configured as at least two separate reaction zones (13',13") having identical internal diameter (d) to correspond together the diameter (V2 d) of the un-separated reactor zone (5), in that the two separate reaction zones (13', 13") having a common freeboard region (14) with separate gas plenums (16) including ash removal pipes (17), and in that a separating member (19) is disposed between the at least two separate reaction zones (13', 13") having a transfer port (20) so as to maintain a continuous inter-transfer of bed material and gaseous reactants between the at least two separate reactor zones (13', 13").
2. The gasification reactor as claimed in claim 1, comprising an exit (18) disposed at tha bottom of the gasifier (1) for discharge of ash outputting from the two reaction zones (13', 13").
3. An improved pressurized fluidized bed gasifier adaptable, in particular in a coal based combined cycle power plant, as herein described and illustrated with reference to the accompanying drawings.

This invention relates to an improved pressurized fluidized bed gasifier adaptable, in particular in a coal based combined cycle power plant, comprising; means for entry of coal into the gasifier (1); means for entry of fluidizing media into the gasifier (1); means for ash removal disposed at the bottom of the gasifier (1) being flowably connected at one end with the reactor zone, the other end leading to a bottom ash discharge port. The fluidized bed reactor zone of the gassifier (1) is configured as at least two separate reaction zones (13',13") having identical internal diameter (d) to correspond together the diameter (√2 d) of the un-separated reactor zone (5), in that the two separate reaction zones (13', 13") having a common freeboard region (14) with separate gas plenums (16) including ash removal pipes (17), and in that a separating member (19) is disposed between the at least two separate reaction zones (13', 13") having a transfer port (20) so as to maintain a continuous inter-transfer of bed material and gaseous reactants between the at least two separate reactor zones (13', 13").