Abstract:
An apparatus for constant feeding of pulverized fuels at ambient or elevated pressure having a fixed restrictor device in the pulverized fuel conveyor line connecting a metering vessel to a pulverized fuel consumer is provided. The restrictor device effects a compensation and also attenuation of pressure fluctuations such as occur in the pulverized fuel conveyor line, in particular during operations to replenish the metering vessel. Special embodiments relate to a further equalization by means of injections of auxiliary gas into the pulverized fuel conveyor line.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of German application No. 102011077910.8 DE filed Jun. 21, 2011. All of the applications are incorporated by reference herein in their entirety. 
       FIELD OF INVENTION 
       [0002]    An apparatus for constant feeding of pulverized fuels at ambient or elevated pressure to a pulverized fuel consumer with compensation and also attenuation of pressure fluctuations in the pulverized fuel conveyor line is provided. 
       BACKGROUND OF INVENTION 
       [0003]    Methods and apparatus for the regulated feeding of pneumatically conveyed pulverized fuels to a consumer load, in particular for the regulated feeding of pulverized fuels into pressurized gasification reactors, are disclosed. 
         [0004]    What is to be understood by pneumatically conveyed pulverized fuels are coals of the most diverse coalification ranks that have been ground into fine powder form, cokes, thermally pretreated biomasses where applicable, or comminutable industrial, commercial and household residue and waste materials. Inorganic pulverized materials, such as are used for example for refining iron ore and for desulfurization, are also included among the possible materials conveyed. 
         [0005]    The pneumatic conveyance of pulverized fuels is known in entrained-bed pressure gasification for the purpose of producing energetic gases and synthesis gases or in the feeding of pulverized coal into the tuyeres of blast furnaces. In this case the pulverized coal is fed via a pressure lock hopper to a metering container that is subject to process pressure, from which the pulverized coal is fed to the consumer load via one or more conveyor lines as a pulverized fuel/carrier gas suspension with a high loading density between 250-450 kg/m3. Entrained-flow gasifiers, tuyeres of blast furnaces, combustion boilers or apparatus for refining iron are to be understood as consumer loads, with use being made of inorganic pulverized materials. 
         [0006]    Any oxygen-lean gases for combustible pulverized materials, in particular inert gases, such as nitrogen or carbon dioxide for example, which are free of condensable constituents, such as water vapor for example, can be used as reducing gas for the pressure locks and as carrier gases. 
         [0007]    The aim to be aspired with the cited technologies is to keep the flowing pulverized fuel volume constant to a high degree per unit time so as not to disrupt the process that is to be fueled. In particular the discontinuous replenishment of the metering container from the pressure locks generates pressure fluctuations which disadvantageously affect the pressure differential that serves as driving force for the conveyance between metering container and consumer. Changes in the volume of material to be conveyed result in oscillations occurring which only level off and subside after a relatively long period of time. In the patent DE 10 2005 047 583 B4 it is therefore proposed to compensate for pressure fluctuations and attenuate occurring vibrations through the regulated feeding of auxiliary gas in immediate proximity to the conveyor line inlet in the metering vessel or into the conveyor line. This technique has proven worthwhile, though it has the disadvantage that considerable quantities of auxiliary gas are fed to the carrier gas. Said auxiliary gas is likewise fed to the consumer load and detrimentally affects the product that is to be produced. When nitrogen is utilized as a carrier and auxiliary gas, for example, the nitrogen content of the synthesis gas increases in the course of the pulverized coal gasification process. 
       SUMMARY OF INVENTION 
       [0008]    The specification discloses an apparatus for constant feeding of the material to be conveyed to the consumer load by means of which differential pressure fluctuations between metering container and consumer load, and consequently volume fluctuations, are compensated while at the same time volumes of auxiliary gas are reduced. 
         [0009]    The object is achieved by means of an apparatus having the features of the claims. 
         [0010]    The proposed solution provides an apparatus for metering and feeding pulverized fuels under pressure to a consumer load, for example pulverized coal to an entrained-flow gasifier, wherein the pulverized material to be conveyed is fed from an operating bunker which is at normal pressure, and is fed alternately via pressure locks to a metering vessel in the lower part of which fluidizing gas is fed by way of a turbulence plate in order to produce a dense fluidized bed into which there are immersed horizontally or vertically one or more conveyor pipelines through which the material to be conveyed is fed continuously to a pressurized consumer/consumer load  2 , for example a pressure gasification reactor. In order to eliminate or attenuate differences in pressure between the metering vessel and the consumer load, a fixed and where appropriate controllable restriction point is incorporated into the pulverized fuel conveyor line. As a result the auxiliary gas feed can be dispensed with or at least limited. The restriction point can be positioned upstream or downstream of an auxiliary gas feed that may be disposed therein. Auxiliary gas can also be fed directly to the conveyor line via the restriction point. An overlapping of control processes can be precluded by the feeding of auxiliary gas. Without an auxiliary gas feed, a controllable restriction point, e.g. in the form of a control valve, is advantageous. 
         [0011]    The pulverized fuel flow is measured in the conveyor pipe, the ascertained measured value parameterizing the control variable for the volume of fluidizing gas to be set by way of the control valve  3 . 3  and where applicable the position of the control valve  3 . 8  as well as for the volume of auxiliary gas to be set by way of the control valve  3 . 3 . It is furthermore advantageous to dimension the flow velocity of the pulverized fuel flow in the conveyor lines in the range between 2 to 8 m/s. Since the flow velocity in the restriction points is increased severalfold, it is advisable to implement said restriction points in a wear-resistant form. 
         [0012]    Significant advantages of the claimed apparatus compared with the prior art consist in the ability to compensate for fluctuations in the pressure differentials serving as driving force for the pulverized fuel flow between metering vessel and consumer or pressure fluctuations in the consumer through the installation of a fixed and where appropriate controllable restriction point in the conveyor line(s), with or without auxiliary gas supply. At the same time a constant pulverized fuel flow can be ensured, for example during replenishment processes, from the pressure lock to the metering vessel. The conveyor lines leading out of the lower part of the metering container can be arranged horizontally or vertically. The pressure in the conveyor lines can range between 0.1 and 6 MPa (1 and 60 bar). The conveyor line diameter can be selected between 10 and 80 mm as a function of the conveyor capacity and the number of conveyor pipes. Cross-section-generating apparatus causing no substantial change in the flow direction, such as venturi tubes, diaphragms and the like, are suitable in particular as fixed flow restrictors. In the case of controllable flow restrictors, cavities which lead to the accumulation of pulverized fuel deposits are to be avoided. 
         [0013]    If a plurality of pulverized fuel conveyor lines are fed from a metering vessel, the feeding of fluidizing gas to the individual pulverized fuel conveyor lines can potentially result in a mutual influencing of the pulverized fuel volumes in the pulverized fuel conveyor lines. The apparatus counteracts the mutual influencing of the pulverized fuel volumes in the pulverized fuel conveyor lines. 
         [0014]    Advantageous developments are disclosed in the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Two figures and two examples are referenced below, an entrained-flow gasification process having been chosen as reference object. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0016]      FIG. 1  shows the schematic layout of the technology for pulverized fuel metering under pressure with a fixed restriction point with and without auxiliary gas feed. 
         [0017]      FIG. 2  shows the schematic layout of the technology with pulverized fuel control valve. 
         [0018]    In the figures, like reference signs denote like elements. 
       Example 1 
       [0019]    An entrained-flow gasification reactor  2  according to  FIG. 1  is operated at a pressure of 4 MPa (40 bar), delivering a power output of 500 MW. Toward that end, pulverized bituminous coal reduced to a grain size of &lt;200 μm is fed at a volume rate of 90 Mg/h. For this purpose, the pulverized coal is fed from an operating bunker to a plurality of pressure locks (operating bunker and pressure locks not shown) in order to place the pulverized bituminous coal under process pressure by pressurizing the same with an inert gas. The fill level in the metering vessel  1  is regulated via a fill level controller LIC  3 . 1 . If the fill level in the metering vessel  1  has dropped to a minimum value, the vessel is replenished from the pressure lock. One or more pressure locks can be arranged as a function of the volume of pulverized fuel that is to be conveyed. The pulverized fuel conveyor lines  3 . 2  project vertically from above into the lower part of the metering vessel  1 , in which a very dense fluidized bed having densities of up to 450 kg/m3 is produced by feeding fluidizing gas  3 . 3  by way of a turbulence plate. Applying a pressure differential between the metering vessel  1  and the gasification reactor  2  induces the pulverized coal/carrier gas suspension generated in the fluidized bed to flow to the gasification reactor  2  via the conveyor lines  3 . 2 . According to  FIG. 1 , three conveyor lines  3 . 2 , each having a conveying capacity of 30 Mg/h, are operated in this example, said conveyor lines leading to the three burners  2 . 1  of the gasification reactor  2 . In order to attenuate differential pressure fluctuations between the metering vessel  1  and the gasification reactor and thus keep the conveying capacity in the pulverized fuel conveyor lines  3 . 2  constant, a fixed restrictor device  3 . 6  is arranged in the conveyor line. Venturi tubes, diaphragms, tube reducers and permanently installed non-control valves are suitable as a fixed restrictor device  3 . 6 . Auxiliary gas can be introduced to the restrictor devices  3 . 6  immediately downstream of the conveyor pipe inlet  3 . 7  or in front of, behind or directly into the fixed restrictor device, as indicated in the drawing for example for the pulverized fuel conveyor line shown at the top. The volume of pulverized fuel conveyed in the pulverized fuel lines  3 . 2  is measured in  3 . 5 , the measurement simultaneously parameterizing the control variables for the control valve  3 . 3  for the fluidizing gas volume and where applicable for the control valve  3 . 4  for the auxiliary gas volumes into the auxiliary gas feed in  3 . 6  and  3 . 7 . 
       Example 2 
       [0020]    An entrained-flow gasifier  2  according to  FIG. 2  is operated under the same conditions as in example 1. The restriction point  3 . 8  is in this case arranged as a pulverized fuel control valve in immediate proximity to the gasification burner  2 . 1 . The position of the pulverized fuel control valve  3 . 8  is influenced by the control signals from the volume measurement  3 . 5 . It is also possible to feed auxiliary gas to the conveyor pipes  3 . 2  in addition via the auxiliary gas injection point  3 . 9  and/or at the conveyor pipe inlet  3 . 7 , also controlled by way of the volume measurement  3 . 5 . Wear-resistant implementations being designed and constructed to avoid the accumulation of pulverized fuel deposits and hence blockages are suitable as pulverized fuel control valves  3 . 8 . 
         [0021]    In a special embodiment variant the measurement of the pulverized fuel flow ( 3 . 5 ) is realized between the metering vessel  1  and the pulverized fuel control valve ( 3 . 8 ). 
         [0022]    In a special embodiment variant the fed auxiliary gas influences the pressure differential between the metering vessel  1  and the pulverized fuel consumer  2  in addition to the fixed restrictor device  3 . 6  and is used as a control variable for the conveyance of the pulverized fuel. 
         [0023]    In a special embodiment variant the pulverized fuel control valve compensates for pressure fluctuations in the pulverized fuel conveyor line  3 . 2  and ensures a constant flow of pulverized coal in the pulverized fuel conveyor line  3 . 2 , with or without auxiliary gas. 
         [0024]    In a special embodiment variant the pulverized fuel flow is fed to the burners  2 . 1  of a pressure gasification device  2  as pulverized coal. 
         [0025]    In a special embodiment variant the pulverized fuel flow is fed to the tuyeres of a blast furnace as pulverized coal. 
         [0026]    In a special embodiment variant the pulverized fuel flow represents an inorganic material which is fed as a refining agent to a method for steel production. 
         [0027]    In a special embodiment variant the diameter of the conveyor lines  3 . 2  ranges between 10 and 80 mm. 
         [0028]    While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.