Feed System

Abstract

Transport system for the introduction of biomass into a gasifier comprising: a plug screw that forces the biomass into the gasifier, wherein the plug screw is formed such that the biomass is compressed in order on the one hand for it to be conveyed against a pressure in the gasifier and, on the other hand, to leave the gas and bed material in the gasifier, having a gate valve adjacent to the plug screw and which closes when the plug screw stops so that heat, vapour and gas cannot escape.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/EP2007/058034 filed Aug. 2, 2007, which claims priority of DE 10 2006 039 622.7 filed Aug. 24, 2006, both of which are incorporated by reference.

FIELD OF THE INVENTION

The invention concerns a system for feeding biogenic feedstock into a gasifier, more particularly into a pulse gasifier in accordance with applications DE 10 2006 022 265.2, DE 10 2006 017 355.4, DE 10 2006 017 353.8.

BACKGROUND

The development of thermal gasification processes has produced essentially three different types of gasifier, the entrained flow gasifier, the fixed bed gasifier and the fluidized bed gasifier.

Originally, the fixed bed gasifier and the fluidized bed gasifier were developed for the commercial gasification of biomasses.

The Carbo-V method will be illustrated here by way of an example for the many different technical approaches to fixed bed gasification.

Literature for fluidized bed gasification which is a component of this application may be taken from the following reference: “High-Temperature Winkler Gasification of Municipal Solid Waste”; Wolfgang Adlhoch, Rheinbraun AG, Hisaaki Sumitomo Heavy Industries, Ltd., Joachim Wolff, Karsten Radtke (Speaker), Krupp Uhde GmbH; Gasification Technology Conference; San Francisco, Calif., USA; Oct. 8-11, 2000; Conference Proceedings.

Literature for a circulating fluidized bed in a network system may be taken from the following sources: “Decentralized heat and power generation based on biomass gasification”; R. Rauch, H. Hofbauer; Presentation at University of Leipzig 2004. “Circulating fluidized bed, gasification using air,

Operation Experience with CfB-Technology for Waste, Utilisation at a Cement Production Plant” R. Wirthwein, P. Scur, K.-F. Scharf-Rüdersdorfer Zement GmbH, H. Hirschfelder-Lurgi Energie und Entsorgungs GmbH; 7th. International Conference on Circulating Fluidized Bed Technologies; Niagara Falls, May 2002.

Literature for the combination fixed bed (rotating tube) can be taken from the following sources: 30 MV Carbo V Biomass Gasifier for Municipal CHP; The CHP Project for the City of Aachen, Matthias Rudloff; Presentation Paris, October 2005

Literature for combination fixed bed gasification (slagging gasifier) can be taken from the following sources: Operation Results of the BGL Gasifier at Schwarze Pumpe, Dr. Hans-Joachim Sander SVZ, Dr. Georg Daradimos, Hansjobst Hirschfelder, Envirotherm; Gasification Technologies 2003; San Francisco Calif., Oct. 12-15 2003; Conference Proceedings

Gasification takes place over two stages in the Carbo-V process. First the biomass is split into its volatile and solid constituents at 500° C. This results in a gas containing tar and also “char”. The gas is burnt at temperatures in excess of 1200° C., which breaks down the tars into CO2 and H2. A synthesis gas containing CO and H2 is then generated from the hot flue gas and the char.

These types of gasifier are completely unsuited to the gasification of biomass (which occurs regionally and has a significant influence on the costs in terms of logistics and processing) because of the great technical effort and high economic costs demanded by the high pressure level (up to 40 bar).

Fluidized bed gasifiers may be subdivided into two processes which differ in the heating of the fluidized bed, the circulating fluidized bed gasifier and the bubbling fluidized bed gasifier.

Literature relating to desulphurization in fluidized bed gasification can be found in the following source: Gasification of Lignite and Wood in the Lurgi Circulating Fluidized Bed Gasifier; Research Project 2656-3; Final Report, August 1988, P. Mehrling, H. Vierrath; LURGI GmbH; for Electric Power Research Institute, Palo Alto, Calif.: ZWS-Druckvergasung im Kombiblock, Schlussbericht (Circulating fluidized bed high-pressure gasification in a combiblock, final report) BMFT FB 03 E 6384-A; P. Mehrling, LURGI GmbH; Bewag

An allothermal circulating fluidized bed gasification plant was brought on stream at the start of 2002 in Güssing (Austria). The biomass is gasified in a fluidized bed using steam as the oxidizing agent. A proportion of the char created in the fluidized bed is burnt in a second fluidized bed to provide the heat for the gasification process. A synthesis gas is generated by gasification in steam. The disadvantages are the high acquisition costs for the process engineering and excessive costs for process control.

The management of the fluidized bed material demands a specific regulation and control system for steam circulation in the form of an gas lift pump motion to enhance the exchange of heat and material and to improve the reaction conditions by increasing the effective reaction space. The gas lift pump is a materials handling device in which solid matter/water mixtures are conveyed with the help of compressed air (driving or conveying gas) for instance by means of the injection of this gas through nozzles in pipework or in a stirred tank. The injected gas causes a reduction in the suspension density and hence an increase in buoyancy. Together with the added kinetic energy, this results in conveyance.

A circulation flow results in the containers as the flow.

This is thus transferred to the solids/gas suspension of the fluidized bed.

This principle is transmitted in the present case to the gas/solids suspension of the fluidized bed in the steam converter.

All these systems require a transport system to deliver the biogenic feedstock to the gasifier. The invention below describes a system comprising the processes for delivering the biogenic feedstock into a gasifier, in particular into a pulse gasifier.

The feedstock covers a broad palette. These may be extruded material, round pellets such as are created by pelleting machines, for instance, or biogenic media from agriculture (cereals).

Characteristic for these biomasses are carbon contents in the original material in the range of 40 to 50% by mass with hydrogen contents in the range up to 6% by mass and oxygen contents in the range from 40 to 50% by mass. The calorific values of the feedstock are typically in the range up to 20 MJ/kg. The bulk material densities vary over the range from 200 to 700 kg/h. In addition to a certain proportion of fines, extruded materials have a diameter between 5 and 10 mm with a length from 10 to 20 mm and lump material has dimensions in the area of 20×30 mm with a thickness of up to 10 mm.

SUMMARY OF THE INVENTION

An embodiment of the invention provides a transport system which delivers the biomass to the reactor efficiently taking into consideration the particular characteristics of the reactor.

The process sequence comprises the following steps that are performed with the appropriate equipment.

a. Buffer:

Buffering in a silo (bunker) as a prior step to feeding and metering. Feedstock from different stores may be conveyed to this buffer.

b. Metering and Feeding to the Points of Delivery into the Gasifier:

Taking the net gas production acting as a setpoint value as a basis (result from the control regime for the steam reforming gasifier), the feedstock is metered and distributed to one, two or more points of delivery such that the gas production required results. The system also provides the function of the plug screw which acts as a pressure seal for the reactor system. The system has the flexibility to fulfil these tasks while the broad range of feedstock is being used.

c. Sealing the Reaction System Against the Atmosphere:

A pressure seal for the reactor provided by the material plug formed in the plug screw and a multi-stage system of cellular wheel feeder and gate valve before and after the plug screw and pressurizing the feed tube with N2 (nitrogen) or CO2 (carbon dioxide) may be necessary depending on the reactor type.

This material plug is continuously created in the plug screw which acts as the feed device for the gasifier by adjustment of the volumes. The feed screws are controlled so that the mass flow and the permanent formation of the sealing plug is ensured.

This system is furthermore characterised in that the plug screw(s) is/are equipped in their forward section with a system of nozzles operating in a similar fashion to a jet pulse system, as is known from filter technology.

The plug screw is further equipped with cooling devices for the shaft and the jacket. (It is optionally possible to cool the shaft vanes on this plug screw).

d. Prevention of the Return Flow of the Fluidized Bed Material into the Feed and Metering System when the System is at a Standstill and when the Feed and Metering System is not Operating:

When the gasifier is operating the material is fed into a dense, fluidized bed. Measures are taken to prevent the backflow of bed material into the plug screw when the feed screw is at a standstill, particularly in the start up and shut down processes. To this end, the system is equipped with a gate valve that operates through the material being conveyed and shuts off the flow in a suitable manner. This equipment also permits the plug screw(s) to be drained through a drainage arrangement as a precaution against the sort of backfires that cannot be excluded in the case of brief shutdowns of the otherwise hot gasifier.

Thanks to these various aspects, the system is suited to transporting into the reactor all feedstock coming into consideration for gasification. Because of its particular characteristics, the system is also capable of feeding into internal pressures up to 5 bar.

It is clear from the above that the feed and metering system comprises, in a preferred embodiment of the following elements:

• • a buffer with regulated discharge unit;
  • a metering screw(s) that doses the volume fetched from the buffer;
  • a transport screw to transport the material to the plug screw;
  • a cellular wheel feeder, gate valve before and after a plug screw and a plug screw.

The volume of gas produced depends on (is proportional to) the volume of feedstock. This physical dependency is used as a control for the volume fed. Measurement of the volume of syngas, or the comparison between the setpoint value specification and the volume of syngas measured, is used as the managing closed loop control for the volume of feedstock. As may be seen from the drawings, these variables act directly on the metering screw (single, parallel or multiple arrangement). This screw/these screws is/are fed under the control of the discharge and metering screw from the buffer bunker and these control elements too are incorporated in the control loop together with a fill level monitor in the feed chute to the metering screw(s).

The following transport screws, not regulated in one possible embodiment, convey the feedstock to the actual feed system.

The full control loop concept thus comprises feeding biogenic feedstock into a gasifier for allothermal gasification with the heat of reaction for the gasification reaction being generated in special pulse burners.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic overview of the invention;

FIG. 2 shows the schematic structure of the metering screw and the plug screw;

FIG. 3 shows the plug screw in detail.

PREFERRED EMBODIMENTS

The control concept comprises the specification by the volume of synthesis gas for metering the feedstock through regulated discharge from a buffer and speed-regulated metering screws with monitoring of the fill level of the supply chutes, distribution to the feed devices and formation of the shut-off plugs in the speed-regulated feed screws, with their speed being regulated by the master controller and the fill level monitoring in the supply to the feed system. This feed system (for solids) constitutes substantial progress in fluidized bed gasification.

The discharge system 1 (FIG. 1) comprises a screw 3, the rotation speed of which is regulated by the master controller 2, and which is mounted centrally in the buffer bunker 4. The entire screw is moved over the silo base by means of a rotary drive 5, itself also speed-regulated. Speed regulation is configured such that the fill level of this screw is maintained at a constant level by the screw turning into the material held in the silo. This means that the delivery rate is directly proportional to the speed of rotation of the screw and hence this discharge system is suitable for feed regulation. The current consumption of the rotatably mounted screw that is directly proportional with the torque of this screw is used as the reference variable for the speed control.

The volume is determined by the master control as a function of the setpoint value for the synthesis gas 7 by means of a metering screw. The volume fetched from the buffer silo is metered accordingly.

One or more transport screws 8 transport the volume to the plug screws 9.

The feed system comprises a cellular wheel 10, gate valve 11 upstream of the screw for onwards conveying and simultaneously shutting off both in start-up and shut-down operation and for feeding the plug screw 9. The system is equipped with a system 12 (see FIG. 3) for pressurizing it with air as a sealing medium and/or an inert gas such as N2 or CO2 or steam (the latter medium also acting as an extinguishing and sealing medium). As is clear from FIG. 2, the system comprises the plug screw itself, in which the material plug is generated to plug the pressure. The screw is designed such that this material plug remains stable across the entire speed range and hence with variable volumes of feedstock. This feedstock is conveyed directly into the hot fluidized bed via the gate valve that remains open during operation through a smooth, heat resistant pipe.

Furthermore, the screw includes cooling equipment 13, 14 for cooling the screw shaft 14 and optionally the screw vanes and the jacket 13 in which the screw is fitted. This can be shaft cooling and jacket cooling.

One part of the system is the gate valve 15 directly between the feed screw and the gasifier 16 that is closed when the screw is shut down and prevents the inert bed material flowing back into the screw.

This gate valve is made from heat resistant material as it is located at the interface between the gasifier which is hot in operation and the cooled screw. This measure also prevents backflow during the operational phases in which the feedstock plug being fed does not itself establish the isolation.

The feedstock is supplied to the feed screw by way of a chute 17, cellular wheel feeder 10 and gate valve 11. The fill level monitoring 18 in this feed line guarantees the necessary permanent formation of a material plug for the feedstock throughput configured through the main control system. The arrangement of the cellular wheel feeder and gate valve upstream of the screw furthermore permits the introduction of a sealing gas (air or inert gases such as CO2, nitrogen or steam in exceptional cases).

Gate valve 11 permits an additional gas-tight seal.

A pressure range of the reaction system of up to 5 bar overpressure, as a rule 1.5 bar overpressure, is hence controllable.

Claims

1. Transport system for the introduction of biomass into a gasifier comprising:

a plug screw that forces the biomass into the gasifier, wherein the plug screw is formed such that the biomass is compressed in order on the one hand for it to be conveyed against a pressure in the gasifier and, on the other hand, to leave the gas and bed material in the gasifier,

having a gate valve adjacent to the plug screw and which closes when the plug screw stops so that heat, vapour and gas cannot escape.

2. The transport system according claim 1, wherein a cooling system cools the plug screw from the inside or the outside.

3. The transport system according claim 1, wherein one gate valve is arranged upstream of the plug screw and one gate valve is arranged downstream of it.

4. The transport system according claim 1, whereby a cellular wheel feeder is mounted before the plug screw onto which a feed chute abuts.

5. The transport system according claim 1, whereby the plug screw is equipped in its forward area with a system of nozzles that operates in a similar fashion to a jet pulse system.

6. The transport system according claim 1, whereby a sealing gas may be introduced into the casing of the plug screw, more particularly N2 (nitrogen) or CO2 (carbon dioxide) is supplied to the injection tube.

7. The transport system according claim 1, whereby a buffer that operates with a regulated discharge unit, is connected upstream of the plug screw.

8. The transport system according claim 1, whereby the discharge system comprises a screw mounted centrally in the buffer silo and regulated by a controller.

9. The transport system according claim 8, whereby the entire screw can be moved over the floor of the bunker, also by means of a speed-regulated rotary drive.

10. The transport system in accordance with claim 1, whereby one or more metering screw(s) meter the biomass that is fetched from the buffer bunker and, where necessary a transport screw transports the biomass to the plug screw.

11. The transport system i according claim 1, whereby a control unit that calculates the volume of gas produced proportionally to the feedstock so that this physical dependence can be used as a control for the volume of material fed so that the measurement of the synthesis gas volume, or the comparison between the specified value and the measured volume of syngas produced may be used as the managing control for the volume of feedstock.

12. Method for the introduction of biomass into a gasifier comprising:

introducing of the biomass by way of a plug screw whereby the plug screw is regulated such that the biomass is compressed in order on the one hand for it to be conveyed against a pressure in the gasifier and, on the other hand, to leave the gas and bed material in the gasifier,

Closing of a gate valve adjacent to the plug screw and which closes if the plug screw stops so that heat, vapour and gas cannot escape.

13. The method according claim 12, wherein a cooling system cools the plug screw from the inside or the outside.

14. The method according claim 12 whereby one gate valve is mounted upstream of the plug screw and one is mounted downstream of it and these are closed as a function of the supply or removal of the biomass.

15. The method according to claim 12 whereby a cellular wheel feeder is mounted upstream of the plug screw onto which a feed chute abuts wherein the feeder is controlled such that the plug screw is continuously supplied with biomass.

16. The method according claim 12 whereby the plug screw is equipped in its forward area with a system of nozzles that operates in a similar fashion to a jet pulse system to inject into the biomass.

17. The method according claim 12 whereby a sealing gas is introduced into the jacket of the plug screw, more particularly N2 (nitrogen) or CO2 (carbon dioxide) is supplied under pressure to an injection tube to prevent the occurrence of a drop in pressure.

18. The method according claim 12 whereby the plug screw is supplied from a buffer by a regulated discharge unit.

19. The method according claim 12, whereby the discharge system comprises a screw mounted centrally in the buffer silo and regulated by a controller.

20. The method according claim 19, whereby the entire screw is moved over the floor of the bunker, also by means of a speed-regulated rotary drive.

21. The method system according claim 12, whereby one or more metering screw(s) meter the volume that is fetched from the buffer bunker and, where necessary a transport screw transports the biomass to the plug screw.

22. The method according claim 12 whereby a control unit calculates the volume of gas produced proportionally to the feedstock so that this physical dependence can be used as a control for the volume of material fed so that the measurement of the synthesis gas volume, or the comparison between the specified value and the measured volume of syngas produce may be used as the managing control for the volume of feedstock.