DE3046249A1 - Solid bed pressurised gas generator with increased output - achieved by controlling size of coal briquettes, ash temp., and speed of ash removal - Google Patents

Abstract

Generator is used for the gasification of brown or mineral coals which may vary widely in their coking properties. The amt. of coal which can be fed down the generator shaft is increased by using the size of the coal particles (e.g. briquettes) as a parameter for process control. The stability of the solid bed is maintained by keeping the velocity of the gas fed through the bed at a level below that causing fluidisation of the coal. Optimum conditions of gasification are pref. achieved by controlling the temp. of the ash obtd. from the coal, and also by varying the speed at which the ash is removed from the base of the generator. A computer is pref. used for process control. Automatic process control can be employed to increase the productivity of the generator.

Description

a) Title of the invention

Procedure for increasing the specific shaft loading of fixed loads Pressure gas generators b) Field of application of the invention The invention relates to a Procedure to increase the specific shaft clearance and to optimize the Process implementation of fixed bed pressure gas generators for the gasification of brown or hard coal of various degrees of coal.

The usual specific shaft loads are exceeded. In the gasification agent, usually an oxygen-steam or an air-steam mixture, is the non-oxidizing part is minimized.

The method should preferably be used where the Nature of the charcoal, the mineral substance it contains in the case of gasification below the ash melting point, a very fine-grained and powdery one Structure experiences and the gasification substance during the process run strongly to the Tends to disintegrate and form fine grains.

c) Characteristic of the known technical solutions: It is general known that the determining factor in fixed bed gasification to define the performance limit The main factor is the dust discharge that occurs.

To minimize this disruptive phenomenon in the process flow, the depending on the specific properties of the fuel at very different performance limits can occur, are already a number of constructive and procedural Suggestions have been made.

These can be divided into several groups.

For example, you pursue the goal of fueling the fuel before and during the process run to be treated in such a way that by thermal and chemical processes as little as possible Fly dust is created. Such solutions are, inter alia, in the patents DD-PS 26 392, 38 791, 119 814 and in DD-PS C 10 J / 205 413.

Constructive solutions that ensure optimal flow distribution in the upper part of the reactor, e.g. in the vicinity of the gas outlet, are, among others, in the patents DD-PS 132 980, 110 297, 133 817 and 133819 have been proposed. Just as much attention has been paid in the past to optimizing the Fixed-bed pressure gasification of the structural design and the mode of operation of the rotating grate Dedicated in connection with the supply of the gasification agent. Such suggestions were among others in the patents DDtPS 133 571, 134 243 and in DD-PS C 10 J / 209 772 submitted.

The common concern lies in the proposed solutions of both groups Basically, the flow before the entry and after the exit from the bed to steer in such a way that a distribution that is as even as possible and thus an optimum in the process control is achieved.

The disadvantage of these proposals is connected with the flawed thesis, according to which the flow distribution as a decisive process variable for the performance from Fixed beds, essentially from the upstream and downstream facilities, e.g. Eoble distributors and gas collection rooms or grates, will be influenced. However, this is not the case. Rather, the flow is distributed in particular by the Influences the grain structure resulting in the process.

Very fine-grain layers of bulk material in the reactor can, for example, create a flow resistance assume that the values are several powers of ten higher than the resistance of Can accept fixtures in the gas collection room or on the rotating grate. Furthermore it has fine grain the very disadvantageous characteristic that it is moved in the bed by the fluid and is deposited at any point in the reactor and thus the unevenness the bulk structure potentiated. This can even be used in certain areas of the reactor be brought to total blockage and the flow through the same can only take place in channel form, which practically applies the principle and advantages of the Countercurrent reactor are lifted.

All past actions outlined above are taken therefore only too successful, because their effect on insignificant areas at the beginning and remains restricted at the end of the pour.

Another group of suggestions for improving the process flow in the pressure gasification of coal is concerned with the control of the ash discharge. The main aim here is a more even flow and the avoidance of channel formation can be achieved, which e.g.

also the aim of DD-PS 133 247rist.

Another suggestion with a similar aim is provided by the control system of the ash discharge on the basis of an ash balance at the reactor.

Even with these proposed solutions it is misunderstood that for a uniform Flow through the fixed bed Grain structure in the fixed bed is the decisive factor Represents a criterion for controlling the output at all.

The control of the ash discharge also does not allow keep the fire zone constant because this when the orn structure of the fixed bed is ignored, does not represent a flat surface. This, on the other hand, extends into Form of pronounced channels in which considerable mass flows of solid matter in Flow direction of the fluid can move over large vertical areas of the Fixed bed.

Also the inclusion of an ash balance in a regulation of the ash discharge does not lead to the desired improvements, because when there is a high discharge of solids does not set a level ash bed and fire bed position with the raw gas flow and moreover for a qualitative and quantitative determination of what is entrained with the fluid Solid stream no practically applicable measuring methods are known.

d) Object of the invention: The object of the invention is a method for increasing the specific shaft loading and the improvement of the economy of fixed bed pressure gas generators for the gasification of brown or rock coals of various degrees of coalification, by means of suitable methods for modifying the grain structure such Conditions are created that optimal flow conditions are decisive Prerequisite for a high load capacity of the bed and thus for a high set specific performance with optimal process management and improved economy, This enables process automation in connection with the ash discharge.

e) Statement of the essence of the invention: The invention is the task is based on the previously valid views regarding the influence of generator installations, such as coal distributors, gas collecting rooms or grates, on the flow distribution and thus the associated stagnation in the further improvement of process management to overcome.

According to the invention the object is achieved in that the formation the grain structure in the fixed bed as a decisive reference variable for the process flow depending on the respective process conditions by way of the process run is controlled in such a way that a stable fixed bed and a uniform flow through it the bulk ceases.

The necessary assessment of the grain structure, which in terms of their fluidic quality in general with the characteristics of the average grain diameter dsm and the so-called gap volume is defined, according to the invention based on the criterion vortex point velocity for each height element of the bed of the Reactor made.

The influence of the grain structure in the fixed bed of the reactor can can be done in various ways.

It is first suggested the grain structure which was when gasified accruing ash and that located in the middle part of a pressure gasifier Ash-coke ash - coal - mixture by changing the reaction temperature In the oxidation zone to be controlled. It was operated on large-scale pressurized gasifiers determined that, for example, with the change in the reaction temperature in the oxidation zone not only changes the grain structure of the ash, especially its fine grain content can be, but also the fine grain fraction in the reduction zone, d.b. in the area of the partially gassed coke.

It is advantageous to keep the reaction temperature in the oxidation zone and to increase the reduction zone to such an extent that for at least 30% of the mass fraction of the Mineral substance of the coal of the SSnterbzw. Melting point is exceeded. With the The constant flow through which a fixed bed can be achieved is the cause of the formation of larger slag agglomerates low, because the fine grain fraction, consisting of Ash and coke-ash particles, as a result of not exceeding the vortex point velocity is not shifted to a greater extent by the fluid in higher layers and thus forms easily melting butectics through selection processes. Further by avoiding the transport of fine grain to neighboring areas the chemical-physical token conditions for the process flow are always secured in such a way that that with the same composition of the gasifying agent no different reaction temperature can arise. Thus, the risk of slagging is suppressed to a minimum. If the vortex point velocity in the fixed bed is nowhere near, especially in the oxidation and reduction zone exceeded, the reaction end temperature be increased so much that a higher proportion of the mineral substance in the form of a coarse-grained bulk material is transferred, which is dwrchstrambar.

There is also the fact that the reaction temperature is sufficiently high in the reduction zone due to the beginning sintering processes in the partially gasified coke the grain disintegration and thus the formation of dust are already decisively restricted.

Practical ways of changing the reaction temperature and thus the grain structure in the oxidation and reduction zone are the changes the oxygen content in the gasification agent or

its composition-par excellence and the choice of the temperature of the Gasifying agent.

The exact maintenance of a certain maximum temperature in the oxidation zone, which depends on various factors, is carried out through constant monitoring and control by means of a process computer. This is also necessary in order to on the one hand the advantages of a high reaction temperature should be able to use and on the other hand, to avoid slagging or the accumulation of excessively large pieces of slag.

Auxiliary variables are used to set an optimal reaction temperature according to the invention on the one hand Demperatureneßwerte which are preferably on the inner jacket of the The generator can be removed at the level of the ash zone for the application that reaches it the vortex state in the bed by an unsteady temporal course and Show abrupt changes.

This leaves a grain structure difficult to flow through, d.b. one to recognize low reaction temperature.

On the other hand, as an auxiliary variable for setting an optimal Re act ion temperature the setpoint of the amount of ash to be discharged from the generator, which results from the amount of coal gasified per unit of time in the reactor. If this is not reached, the horn structure in the generator shaft is too fine-grained and there are significant amounts of ash or.

Coke ash particles do not go over the grate, but rather over the raw gas outlet carried out. It is further proposed according to the invention to combine the process sequence with the optimization of the reaction temperature of the oxidation zone with regard to the ash or to control the solids discharge via the mode of operation of the rotating grate in such a way that that there is always a certain equilibrium temperature resulting from the temperature the ash from the oxidation zone and the gasifying agent flowing in the opposite direction results, is complied with.

This temperature is preferably recorded directly in the Reactor and in several places immediately below the oxidation zone on the outside Scope of the reactor. As a reference variable for the ash resp.

Solids discharge is preferably an average temperature, calculated from the average of at least two, preferably 4-6, measuring points.

According to the invention, the control of the pushing mechanism takes place for the solid matter or the ash according to an algorithm that takes the temperature readings, the time behavior of the overall system and the limit values for the equilibrium temperature considered. The reaction temperature also goes into this algorithm in the oxidation zone and that specifically discharged from the reactor per unit of time Aschemeage in connection with the aforementioned auxiliary variables in such a way that always a stable fire bed and an optimal final temperature to be discharged from the reactor Solid amount is guaranteed.

Is preferably used as a target value for the temperature difference between ash to be discharged from the reactor and the entry of the gasification agent, which flows through the ash bed, a value of a maximum of 50 E.

This is an optimal energetic process management, as well a protection of the components, which are usually not completely resistant to thermal damage the discharge organs for the best material reached.

It is also proposed according to the invention in the case of briquetting of the gasification material to add suitable mineral substances to this, whereby the grain structure and thus the fine grain fraction that is harmful to the process sequence It can be influenced that also in the area above the oxidation zone of the reactor a grain breakdown with fine grain formation is largely counteracted.

The most suitable for such additives are those mineral components, which, when exposed to thermal stress, solidify the grain structure of the coal substance lead or

as a result of the gassing process for me alone solid, form a compact structure. Such properties, for example, clay minerals, too Lime, contained in the form of CaO in coal, leads to the formation of sarbonate when heated (CaC03), which leads to a solidification of the structure up to a certain temperature level leads and thus counteracts the iS: ohlebildmg.

Other mineral components or combinations of them also lead in the form of additives or with a certain coal selection or coal mixture naturally to such process-stabilizing effects.

The setting of a high reaction temperature and mixing from minerals to briquetting can have consequences in the form of solidification be connected to a larger extent in the shaft of the generator. Emollient minerals possibly enter bonds with the ski wall, if these are made with ordinary refractory material, e.g. chamotte is hidden.

According to the invention it is proposed that a high reaction temperature be started up in the oxidation zone in connection with a slag-resistant inner lining, preferably with ceramic material, which has a high thermal conductivity, or on a metallic basis.

f @ Exemplary embodiment The invention is intended below using an exemplary embodiment are explained in more detail.

The ash is generally discharged from the generator via a Rotating grate, so-called scrapers are used as discharge organs. The carried out Ash tightness is determined by the cross-section of the scrapers, their number and running speed as well as determined by the term.

The speed of rotation and the duty cycle for the rotating grate run are used in practice as target values for the temporal ash discharge.

According to the invention, the speed of rotation of the is adjusted Rotary grate and the definition of the duty cycle or the change of both variables in such a way that an increase gradually increases in fixed time intervals of the ash discharge is carried out up to the temperature measuring points of the ash zone the permissible temperature as an expression of the permissible temperature difference between Gasification agent and ash preferably up to max.

50 K has been reached.

Is this temperature in the form of an average of several temperature measuring points has been reached in the ash zone, the initial values for the ash discharge are reached is set, which means that a two-point control is automatically applied when the generator is in stable operation the ash bed height in the generator is given. The scheme of this system will be like this schalket that the end positions of the ash bed height only in larger time intervals, preferably in 2 hours.

Takes place within this cycle in the ash zone, in the ash discharge Unsuitable rise in temperature, which indicates that the vortex state has been reached of the fixed bed indicates the reaction temperature in the oxidation zone, preferably by increasing the proportion of oxidizing components in the gasification agent, to increase.

The reaction temperature must also be increased, if independent of the trend of the temperature profile in the ash zone the temporal The amount of ash discharged from the reactor via the grate falls below the setpoint. As is well known, this can be done using appropriate level indicators in the ash sluice to be controlled. The increase in the reaction temperature is also in Make a series of steps that are adapted to the type of coal.

The temperature increase is ended when the setpoint for the ash output or a stable temperature profile has been reached in the ash zone.

By setting a high reaction temperature and mixing From minerals to the briquetting material, damage can occur in the generator shaft, according to the invention by a slag-resistant inner lining, preferably made of ceramic material or on a metallic basis, can be avoided.

Claims (6)

Invention claim 1. A method for increasing the specific shaft loading of fixed bed pressure gas generators for the gasification of brown or hard coal des various degrees of coalification, characterized in that the test size for the process control the Eorn structure in the fixed bed is used and as a criterion for the stability of the fixed bed and thus the uniformity of the flow The vortex point speed is a decisive prerequisite for optimal process control applies to each height element of the reactor, with the permissible flow velocity of the fluid must always be regulated below the vortex point velocity. 2. method according to item 1, characterized in that the change the grain structure, which is determined by the mean grain diameter dsm and the degree of vacancy is defined, in the oxidation and reduction zone, the reaction temperature in the oxidation zone is used, preferably in the bread that is oxidizing Proportions of the gasification agent or its starting temperature by a corresponding Mixture preparation can be changed so that the sintering and melting point of the mineral components the coal using a slag-resistant ceramic or metallic Inner lining of the generator is exceeded. 3. The method according to item 1, characterized in that for an optimal Control of the grain structure in the oxidation and reduction zone via the final reaction temperature First of all, the ash bed temperature measured at the circumference of the reactor as auxiliary variables and secondly, the setpoint, which is derived from the solids balance of the process for the mineral substance to be discharged via the grayling sluice results in this way will, that the discharge speed of the mineral substance over the grate is reduced, when the ash bed temperature rises and vice versa and the reaction end temperature is increased via the change in the gasification mixture if at a high ash bed temperature the amount of ash discharged with the grate is too small. 4. The method according to items 1 and 2, characterized in that the process control in such a way according to an Algoråthmus with the help of a process computer that as The output variable for the ash bed temperature is an average of at least two or several measuring points is used and as a basis for the target value of the Asche the ratio of the sluice operations between the coal sluice and the ash sluice applies, where the reaction temperature is to be increased when the ratio number of Coal transfers to Number of ash transfers exceeds the setpoint. 5. The method according to items 1 and 2, characterized in that for one energetically optimal process management through the mean value of the ash bed temperatures the regulation of the ash discharge is limited to a maximum value of 50 K. is above the temperature of the gasifying agent. 6. The method according to claim 1, 3, 4 and 5 characterized in that that to influence the grain structure of the gasification material in the case of briquetting Mineral substances are mixed in, preferably clays and lime, forming a cause high mean grain diameter or with the selection of coals for the Gasification is worked towards the enrichment of such tomponenten.