GB1558895A - Vertical oven for thermal processing of lump fuel - Google Patents

Description

(54) VERTICAL OVEN FOR THERMAL PROCESSING OF LUMP FUEL (71) WE, NAUCHNO-ISSLEDOVAmL- SKY INSTITUT SLANTSEV, of Narvskoe shosse, 12, Kokhtla-Yarve, and SLANT SEPERERABATYVAJUSCHY KOMBINAT IMENI V.I. LENINA, of Narvskoe shosse, 14, both of Estonskaya SSR, both Union of Soviet Socialist Republics, both corporations organised and existing under the laws of the Union of Soviet Socialists Republics, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : The present invention relates to vertical ovens for thermal processing of lump solid fuels, such as oil shales, to produce a gasvapour mixture.

In view of a possible power crisis there is an increased concern in many countries of the work about the possibility of using the oil shales as a source of manufactured liquid fuel (referred to below as tar). One of the essential problems to be faced with in using large shale deposits on a commercial scale is the provision of a plant with a great unit capacity.

What is desired is an oven which will ensure efficiency in terms of shales varying from 10000 to 15000 tons per 24 hours. The oven should provide uniform heating-up of a solid fuel bed with the resultant enhancement of the tar yield and increase in thermal efficiency of the process.

The present invention provides a vertical oven for thermal processing of lump solid fuel to produce a gas-vapour mixture, comprising: a hollow refractory-lined body of sub stantially constant internal cross-section, defining a semicoking zone, a gasification zone, and a cooling zone arranged in descending series along its height; means for feeding a heat carrier into the semicoking zone through inlets located around the periphery of that zone; means for feeding a heat carrier into the gasification zone through inlets located around the periphery of that zone; a chamber for collecting and discharging the gas-vapour mixture, disposed along the vertical axis of the oven along the entire height of the semicoking zone, and defined by a grating in the form of a pipe; means for charging the lump solid fuel into the top of the semicoking zone around the pipe; and means for discharging solid waste material from the bottom of the cooling zone, which zone has a substantially unoo structed constant cross-section.

It is expedient that the pipe be circular in cross-section.

Such a constructional arrangement appreciably enhances the heat transfer conditions at the point of exit of the gas-vapour mixture from the fuel bed contained in the semicoking chamber. If, for example, the diameter of an oven for processing oil shales is assumed to be 10 m in its crossection and an average diameter of the chamber for collecting and discharging a gas-vapor mixture is equal to 2 m, the cross-sectional outlet area (that of the grating on the "cold" side of the semicoking chamber) will prove to be 5 times less than that of the inlet (at the heat carrier inlet of the semicoking chamber).Moreover, it should be borne in mind that though the volume of the heat carrier decreases by 2.0--2.5 times owing to a drop in the temperature of the heat carrier (from 800-9000C to 150-2000C) which takes place in a shale layer, the heat carrier rate at the outlet of the semicoking chamber will still exceed in the long run that at the chamber inlet also by 2.0-2.5 times.

The heat transfer factor a, will proportionally increase, since the factor can be expressed as:

where WO is the velocity of the heat carrier under normal physical conditions, in m/s; T is the temperature of the heat carrier, in K; andean diameter or and d is the mean diameter of the lumps of shale, in m, (see M.Ya.Gubergats, Thermal Processing ot Kukhersit-Shale, Talling, "Valgas", 1966 P 290).

Hence, in the given case when considering the heat transfer conditions created in a fuel bed at a point of exit of the gas-vapour mixture from the semicoking chamber, value At will decrease, as is the case in the above-outlined oven embodiments, and , on the contrary, will appreciably increase (by 2.0 > 2.5 times).

As a result, the quantity of heat Q=f(.V.At) where ev is the heat transfer factor, in kcal/m3 . h . OC; V is the volume of fuel, in m3; and at is the mean temperature difference be tween the heat carrier and the fuel, in OC that is transferred to the shales in a bed and is in direct relation to the heat transfer factor, will also increase appreciably in comparison with conventional oven designs-by 2.0--2.5 times.

As a result, there will be a marked improvement in the heating up of the fuel on the "cold" side of the semicoking chamber.

Moreover, there are no side walls in the semicoking chamber, as viewed in the direction of the heat carrier flow, the chamber being bounded only by the cylindrical wall, the "wall effect" being thereby avoided here, a feature contributing to the regular distribution of the heat carrier in a fuel bed.

A peripheral arrangement of the heat carrier inlets in a plurality of tiers is also conductive to uniform distribution of the heat carrier in a fuel bed. The heat carrier is obtainable by burning a gas either in furnace devices located in direct proximity to each inlet or in one or a plurality of such furnace devices with subsequent supply of the heat carrier to each inlet individually.

An important advantage lies in the possibility of providing ovens of a large unit capacity for processing oil shales with a relatively low content of organic matter, which have a wide terrestrial distribution. Using a chamber for collecting and discharging a gas-vapour mixture having a constant (along its height) cross-section, the degree of filling the semicoking shaft with shales as high as 8090% can be attained. It stands for a two or four fold increase as compared with prior-art ovens having horizontal-transverse flow of a heat carrier. This design feature opens the way for developing ovens with a capacity of 10000 to 15000 tons of shales per 24 hours.

Another advantage of the oven, namely the simplicity of its embodiment, is also worth noting. Large-capaåty ovens for processing lump shales are distinguished by their great overall dimensions (e.g. 10-12 m in diameter and 30-35 m in height). With such overall dimensions the use of the prior-art design concepts adopted for the ovens with a horizontaltransverse flow of a gaseous heat carrier would call for special purpose appliances to be developed for securing flat metallic gratings at the gas vapour mixture outlet side of semi coking chambers, and for refractory gratings at the heat carrier inlet side. From the stand point of their bearing capacity the flat gratings, when exposed to the shale pressure, are much inferior to curved ones.From design aspects the provision of a high-strength grating in the form of a pipe does not present a problem, the resulting grating being simpler in con struction and less metal-consuming than its flat counterpart.

As for the arrangement of a refractory grating at the gaseous heat carrier inlet side of the semicoking chamber, there is no need for this whatsoever. The absence of a chamber for preparing and distributing a heat carrier, or a furnace device having a great volume, reduces the danger of explosion within the unit and simplifies explosion-preventive measures.

Hence, there are but only extremely limited possibilities of developing units in a capacity range of 10000 to 15000 tons of shales per 24 hours on the basis of the already known design principles followed in the ovens with a horizontal-transverse flow of a gaseous heat carrier. Apart from the complexities of developing the design of certain particular elements of such ovens, it would call for providing units with too large overall dimensions, which would in turn demand unwarrantablv great investments in construction.

The heat carrier inlets of the semicoking and gasifying chamber should preferably constitute distributing chambers, of which each chamber is made in the oven wall at the side of its working space, sealed from the adjacent chamber, reproduces the configuration of said oven wall and is defined at the oven working space side by a louver whose length ensures free egress of solid fuel particles from the bottom part of the chamber and an angle of inclination of louver planes at the side of the oven working space provides for continuous transfer of the fuel along said planes.

The introduction of the heat carrier into a fuel bed through distributing chambers furnished with the louvers set up in the oven brickwork, practically along the entire surface of the semicoking chamber, assures a uniform distribution of the heat carrier within the fuel bed in the horizontal plane of the oven.

Thus, the oven ensures a substantially uniform distribution of heat in a fuel bed both along its width and depth with respect to the direction of the heat carrier flow. Consequently, in this case there is a higher tar yield.

It is advisable for the pipe formed by the grating, mounted in the chamber for collecting and discharging a gas-vapour mixture, to in crease stepwise in the direction of the gasvapour mixture flow, approximately in shape to a truncated cone. The point is that the diameter of the chamber for collectiong and discharging a gas-vapour mixture is selected so as to provide a rather low flow rate of gasvapour mixture within the chamber and, hence, a minimum carry-over of a shale dust from the oven. In this case calculations are performed for the top part of the chamber for collecting and discharging a gas-vapour mixture, where a maximum quantity of the mixture is accumulated, as all the flows of the gas-vapour mixture admitted into the chamber all along its height pass naturally through its top portion.

If the cross-section of the chamber for collecting and discharging a gas-vapour mixture does not change along its entire height, the gas flow rates in the bottom part of said chamber will be naturally lower than those in its top portion, though from the point of view of reducing the dust carry-over from the oven together with the gas-vapour mixture, there is no need for that whatsoever, insofar as the maximum gas-vapour mixture rates in the top part of the chamber have already been chosen to ensure a minimum dust carry-over.

Consequently, the diameter of the chamber for collecting and discharging a gas-vapour mixture can decrease progressively from the top to the bottom part of said chamber, which will provide the possibility of increasing the working volume of the semicoking zone and hence the oven efficiency in terms of shales by 10-15%.

Moreover, owing to a variable thickness of a fuel bed in the oven there is provided substantially uniform heating-up of the bed along the height of the semicoking zone, insofar as with the chamber for collecting and discharging a gas-vapour mixture being larger in diameter in its top portion (as compared with its bottom part) the fuel bed will exhibit here a minimum hydraulic resistance. Such a design promotes more intense heating-up of the treated material in the top part of the oven, i.e. in its semicoking zone, and consequently rapid evaporation of the moisture contained in the shales. On being admitted into the zone of intense semicoking, the thus prepared shales can be thereby effectively subjected to com- plete semicoking within the allotted time, a feature ensuring enhancement of both the tar yield and thermal efficiency of the process.

Thus, in contrast to the prior-art units the herein-proposed oven featuring a rather simple design makes it possible to attain a high efficiency in terms of shales (10000 to 15000 tons of shales per 24 hours), and enhance the tar yield and thermal efficiency of the process.

Moreover, the oven is suitable for processing oil shales with a relatively low content of organic matter, which are most widely distributed over the globe.

The invention will be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic vertical section through an oven for thermal processing of lump fuel; Figure 2 is a cross-section on 11-Il in Figure 1; Figure 7 is a diagrammatic view along arrow A in Figure 1 with certain parts omitted for clarity; Figure 4 is a diagrammatic vertical section through another oven for thermal processing of a lump fuel; Figure 5 shows a plan view and partial cross-section on line V-V in Figure 4 and a top view; and Figure 6 is a diagrammatic side view of a cyclone furnace along arrow B in Figure 4.

In the drawings, solid arrows identify a fuel gas, broken arrows identify air, and chaindotted arrows identify a heat carrier.

Referring first to Figures 1 to 3, the vertical oven for thermal processing of lump fuel, oil shales in particular, comprises a body 1 and having a cylindrical configuration, with a lining 1' of a refractory material enclosed in a sealed metallic casing 2. The body 1 accommodates a semicoking zone 3, a gasifying zone 4 and a cooling zone 5 located one after another is descending sequence along the height of the oven.

Secured on a top plate 6 of the oven and arranged in its semicoking zone 3 is a chamber 7, for collecting and discharging a gasvapour mixture, bounded by a metallic grating 8 in the form of a pipe with a circular crosssection. The top of the chamber 7 communicates with a gas offtake (not shown).

At the periphery of the oven there are furnace devices 9 arranged in tiers and adapted for producing a heat carrier, the devices 9 of each tier being displaced in a horizontal plane with respect to those in the next tier at an angle of 450 as shown in Figure 2. Each of the furnace devices 9 shown in Figure 1 comprises a chamber 10 lined with refractory brick and fitted with a burner 11 for producing a flue gas by combusting a fuel gas supplied along a connecting pipe 12. A connecting pipe 13 serves for feeding air. At the outlet of the chamber 10 there is an inlet 14 for a cooled gas obtained by passing the abovementioned gas-vapour mixture through a condensing system (not shown). The cooled gas is employed for adjusting the temperature of the heat carrier constituted by the flue gas.

The heat carrier flows from the upper tier of furnace devices 9 along gas flues 15 directly into the fuel bed in a semicoking chamber 16 defined between the lining 1' of the oven body 1 and the grating 8 of the chamber 7 for collecting and discharging a gas vapour mixture.

This embodiment of the semicoking zone 3 makes it possible to 80-90% filling of the zone 3 with the shales and ensures a uniform heat carrier distribution in the fuel bed. It affords the possibility of attaining a high oven efficiency in terms of shales (up to 10-15 thou.t per 24 hours) along with a relatively high yield of usable products.

The lower tier of furnace devices 9 is adapted for supplying a gasifying agent, such as flue gases or a flue-gas/air mixture, into the gasifying zone 4. The introduction of the gasifying agent enhances the degree of utilization of organic matter contained in the treated shales.

Charging the shales into the oven is effected by way of automatic devices 17 mounted on the oven top plate 6. The number of charging devices 17, e.g. four as illustrated, is chosen to provide uniform distribution of the fuel over the oven cross-section in a horizontal plane.

In the zone 5 adapted for cooling solid waste residue there are devices 18 and 19 for feeding in cooled gas from the above-mentioned condensing system (not shown). The solid residue is discharged from the bottom of the oven by means of a rotating unloading device shown conventionally at 20.

The above-described oven is used for thermal processing of oil shales in the following manner.

The lump shales are charged by the devices 17 into the semicoking chamber 16, wherein they are heated in a flow of a gaseous heat carrier having a temperature of 500 to 9000C (the temperature is selected in accordance with the quality of the shales) obtained by burning a gas in the furnace devices 9 and mixing the flue gases with the cooled gas introduced through the inlets 14. The heat carrier flows into the semicoking chamber 16 via the gas flues 15 and passes through a descending layer of the shales in a crosswise direction. On heating to a temperature of about 500 to 600 C, the shale is at first subjected to drying, this being followed by the evolution of volatile products.

Upon leaving the semicoking chamber 16, the gaseous heat carrier proceeds together with the semicoking volatile products into the chamber 7 for collecting and discharging a gasvapour mixture to be drawn off at a temperature of not more than 150 to 2000C into the condensing system (not shown insofar as it has no direct bearing on the oven design). As the flow rate of the heat carrier at the "cold" side of the semicoking chamber appreciably increases, the heat transfer conditions are liable to improve greatly irrespective of a temperature drop in flow of gas. This improvement contributes to both a higher tar yield and enhanced thermal efficiency of the process.

From the semicoking chamber 16 the semicoke passes further into the zone 4 where is is subjected to gasification under the effect of an appropriate gasifying agent, e.g. flue gases, supplied by the furnace devices 9 of the lower tier. The gas streams formed in this case also pass into the chamber 7 for collecting and discharging a gas-vapour mixture. As for the temperature conditions needed for the functioning of the zone 4, they are selected experimentally.

The processed solid residue is delivered from the zone 4 into the zone 5 where it is cooled to a temperature of 80 to 1000C with a gas introduced through the devices 18 and 19.

Next, it is discharged by the discharge device 20 onto a conveying means to be handled to dumps.

A preferred oven is illustrated in Figure 4.

In this embodiment the chamber 7 for collecting and discharging a gas-vapour mixture is made in the form of a pipe increasing step-wise in the direction of the gas-vapour mixture flow.

This chamber 7 is made up of a plurality of cylindrical gratings 21 fixed rigidly one above the other. The diameters of said gratings 21 decrease gradually towards the bottom part of the oven, the assembled gratings 21 forming a figure approximating to a truncated cone.

Furnace devices 9 of the cyclone type are constituted by chambers 22 lined with refractory brick and fitted with connecting pipes 23, 24, and 25 (Figures 5 and 6) adapted for sup plying respectively air, a fuel gas, and a cooled gas obtained by passing the gas-vapour mixture through a condensing system. In the chamber 22 as shown in Figure 4, flue gases are formed due to the burning of the fuel gas.

These flue gases inrermix with the cooled gas, thereby forming a heat carrier which passes via gas ducts 26 into distributing chambers 27 acting as heat carrier inlets adapted for supplying it into the semicoking zone 3 and the gasifying zone 4. Each of the chambers 27 is arranged in the oven lining 1', facing the oven working space, isolated from the adjacent chamber 27, reproduces the configuration of the oven lining 1', and has an inclined surface 28. Moreover, each chamber 27 is separated from the oven working space by a louver 29 allowing free egress of solid fuel particles from the bottom part of the chamber if they happen to get on the other side of the louver 29.

The chamber 7 for collecting and discharg ing a gas-vapour mixture comprises a convergent duct 30 tapering towards the top part of the oven and terminating in a sleeve 31.

By analogy with the above-described oven shown in Figure 1, the oven shown in Figure 4 is likewise furnished with devices 18 and 19 for feeding a gas cooled in the condensing system (not shown).

This oven is similar in operation to the above-described one with the only difference being that the heat carrier is admitted into the semicoking chamber 16 via the gas ducts 26, distributing chambers 27 and louvers 29.

Such an embodiment makes it possible to pro vide a more uniform distribution of the heat carrier in the horizontal plane of the oven, which ensures higher tar yields.

The heat carrier uniformly infiltrates the layer of shales in a transverse direction, the shales being meanwhile subjected to semicoking. The gas-vapour mixture enters the chamber 7 where the shale dust settles down, whereupon it is passed at a temperature of 1o200 C through the convergent duct 30 and the sleeve 31 into the condensing system (not shown).

The above described embodiment of the semicoking zone 3 enables the degree of filling the zone with shales to be brought to 90 95% and ensures a regular distribution of the heat carrier in the fuel bed using a smaller number of furnace devices as compared with the first oven embodiment described above.

WHAT WE CLAIM IS:- 1. A vertical oven for thermal processing of lump solid fuel to produce a gas-vapour mixture, comprising: a hollow refractory-lined body of substantially constant internal crosssection, defining a semicoking zone, a gasification zone, and a cooling zone arranged in descending series along its height; means for feeding a heat carrier into the semicoking zone through inlets located around the periphery of that zone; means for feeding a heat carrier into the gasification zone through inlets located around the periphery of that zone; a chamber for collecting and discharging the gas-vapour mixture, disposed along the vertical axis of the oven along the entire height of the semicoking zone, and defined by a grating in the form of a pipe; means for charging the lump solid fuel into the top of the semicoking zone around the pipe; and means for discharging solid waste material from the bottom of the cooling zone, which zone has a substantially unobstructed constant cross-section.

2. A vertical oven as claimed in claim 1, wherein the pipe is circular in cross-section.

3. A vertical oven as claimed in claim 1 or 2, wherein the pipe widens in sreps in the direction of the gas-vapour mixture flow.

4. A vertical oven as claimed in any of claims 1 to 3, wherein the means for feeding a heat carrier into the semicoking and gasification zones comprise separate distributing chambers in the wall of the said body, each chamber being separated from the working space of the body by a louver allowing free egress of solid fuel particles, if any, from the bottom of the chamber.

5. A vertical oven for thermal processing of lump solid fuel, substantially as described herein with reference to, and as shown in, Figures 1 to 3 or Figures 4 to 6 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. vide a more uniform distribution of the heat carrier in the horizontal plane of the oven, which ensures higher tar yields. The heat carrier uniformly infiltrates the layer of shales in a transverse direction, the shales being meanwhile subjected to semicoking. The gas-vapour mixture enters the chamber 7 where the shale dust settles down, whereupon it is passed at a temperature of 1o200 C through the convergent duct 30 and the sleeve 31 into the condensing system (not shown). The above described embodiment of the semicoking zone 3 enables the degree of filling the zone with shales to be brought to 90 95% and ensures a regular distribution of the heat carrier in the fuel bed using a smaller number of furnace devices as compared with the first oven embodiment described above. WHAT WE CLAIM IS:-

1. A vertical oven for thermal processing of lump solid fuel to produce a gas-vapour mixture, comprising: a hollow refractory-lined body of substantially constant internal crosssection, defining a semicoking zone, a gasification zone, and a cooling zone arranged in descending series along its height; means for feeding a heat carrier into the semicoking zone through inlets located around the periphery of that zone; means for feeding a heat carrier into the gasification zone through inlets located around the periphery of that zone; a chamber for collecting and discharging the gas-vapour mixture, disposed along the vertical axis of the oven along the entire height of the semicoking zone, and defined by a grating in the form of a pipe; means for charging the lump solid fuel into the top of the semicoking zone around the pipe; and means for discharging solid waste material from the bottom of the cooling zone, which zone has a substantially unobstructed constant cross-section.

2. A vertical oven as claimed in claim 1, wherein the pipe is circular in cross-section.

3. A vertical oven as claimed in claim 1 or 2, wherein the pipe widens in sreps in the direction of the gas-vapour mixture flow.

4. A vertical oven as claimed in any of claims 1 to 3, wherein the means for feeding a heat carrier into the semicoking and gasification zones comprise separate distributing chambers in the wall of the said body, each chamber being separated from the working space of the body by a louver allowing free egress of solid fuel particles, if any, from the bottom of the chamber.

5. A vertical oven for thermal processing of lump solid fuel, substantially as described herein with reference to, and as shown in, Figures 1 to 3 or Figures 4 to 6 of the accompanying drawings.