1. Field of the Invention
The present invention relates to a process for the carbonization of oil shale and/or other carbonizable materials, including a process line serving for carbonization, with a closed cycle and without condensate recovery, wherein the materials flowing through the process line are heated to the carbonization temperature through heat exchange.
Coming into consideration as further carbonizable materials are fuels which are high in inerts such as, for example, bituminous rock, oil-containing fuller's earth, high-ash coal, oil sands, refuse and the like.
2. Discussion of the Prior Art
Numerous processes have already been proposed for the carbonization of oil shale and similar fuel-containing materials having a high proportion of inert materials, for some of which pilot plants have also been constructed. However, it is difficult to completely utilize the fuel content of the raw material and with a satisfactory degree of efficiency since, in essence, subsequent to the carbonization there remains a predetermined proportion of fuel, particularly carbon, in the carbonized material, whose heat of combustion can frequently not be employed, and if so then only with extensive and complex apparatus.
A survey of such processes is elucidated in E/MJ (September 1977) pages 148 through 154. One of the previously mentioned processes is described therein under the designation "Lurgi L.R." In the known process the decarbonized raw material which is conducted through the cycle is employed as a heat carrier. After the carbonization this raw material is pneumatically conveyed into a storage bin, whereby there is burned the so-called fixed carbon so as to lead to an increase in the sensible heat beyond the carbonization temperature. The conveying air, which is concurrently utilized as combustion air for the combustion of the fixed carbon, leaves this process line into the atmosphere at combustion temperature and is lost. Also the heat which is contained in the ash, in effect, in the fully burned-out raw material, is lost.
In another process which is referred to in that publication, ceramic spheres are heated through the combustion of process gas, and which serve as solid heat carriers for the heat which is required during the carbonization process. For the heating of the ceramic spheres there is utilized a special sphere heater whose exhaust gases serve for the preheating of the raw material which is to be carbonized such as oil shale. In this process, the fixed carbon which still remains in the raw material subsequent to the carbonization is not utilized. The carbonized residue leaves the process at the carbonization temperature (approximately 500.degree. C.) and must be cooled by being sprayed with water since it will otherwise continue to burn and represent a significant burden on the environment (for instance, a stench).
Other processes which are mentioned therein utilize carbonization gas which is conveyed in a closed cycle as a heat carrier. This gas is heated either directly through combustion or through indirect heating. Employed as the cycle gas is the incondensible component of the carbonization gases. Thus, the cycle gases are cooled to condensate precipitation, so as to be thereafter again heated for heat transfer for the carbonization process. This results in a significant heat loss with a correspondingly lowered degree of efficiency. A still satisfactory degree of heat is possessed by a process wherein the heat which is transferred to the cycle gas originates from the combustion of the fixed carbon. Even in this process does the ash leave the process at a combustion temperature of about 800.degree. C.
Moreover, there have also been proposed retort processes with indirect heat transfer from the gas to the solid material, however, these have not been found any applicability since the indirect heat transfer of gas/solids material in the required large operating units, due to the large heat transfer surfaces then required, lead to presently uncontrollable constructions.
Additionally, there have also been previously proposed so-called on-site processes in which the raw material is carbonized in its original deposit whereby the fixed carbon should also presently be burned. These on-site processes have also failed to find application in view of the difficulty soluable problems of a controlled process conductance. For such processes for relatively high-yield oil shale, reports have been made of a yield of merely about 50 to 60%.
In the decarbonization of other raw materials, processes have already been proposed which are not suitable for the carbonization of carbonizable material such as oil shale and similar raw materials.
For example, from German Pat. No. 11 60 823 there has become known a process for continuous degassing, such as the carbonization and/or coking of fine-granular, non-caking water-containing fuels through the intermediary of hot gas streams. This process is particularly suited for the production of coke as the primary product, whereas carbonization gas occurs as a side-product which is thinned-out through the combustion gases of the heat generator. For the carbonization of oil shale and other carbonizable raw materials with high contents of inert materials and with an also necessarily low fuel content; however, this process is not suitable since the process residue still contains the fixed carbon and no combustion is provided. Since the residue exists from the process at carbonization temperature, for a large quantity of residue the heat requirement of the process is extremely high whereby so as to also require extremely large quantities of combustion gas in order to be able to maintain the necessary process temperature. The thereby obtained thinning of the carbonization gases reduces the heat value of the noncondensable gases so extensively for introduced low-grade materials, that it practically precludes any utilization of the gases. For fuel-poor, ash-rich materials, such as oil shale or the like, whose commerical utilization is the object of the invention, this process is also not suitable. The same also pertains to a similar known process as well as an arrangement for the continuous thermal treatment, such as degasification and/or coking, of fine-granular water-containing fuels; having reference to German Laid-Open Patent Application 16 71 320. Also in this instance it is impossible to recover an unthinned high-quality carbonization gas. The carbonization gas extensively contains the exhaust gases of an external heat generator.
In another known process for the degasification of powdered fuels (as in German Pat. No. 977,218) there is employed a distillation chamber in which the material is loosened by means of the introduction of CO.sub.2 or steam to a density of 8 to 80 g/l. The introduced gases thin out the product gas. The required heat quantity is conveyed into the distillation chamber through the intermediary of a solid heat carrier from a further similar treatment chamber, and in which there is combusted the remaining carbon and, as occasioned, auxiliary fuel. The excess combustion residue and the exhaust gases from this combustion stage leave the process at the temperature of the combustion stage. The thusly generated high heat losses can only by avoided by extensive additional measures for facilitating utilization of the exhaust gas heat.
Finally, also known is a process and an arrangement for the degasification of fine-granular up to dust-like fuel (refer to German Pat. No. 11 97 432), in which there are employed as essential components at least two air heaters acting as heat exchangers as primarily employed in the foundry industry. This process operates in an alternating manner whereby one of the air heaters is currently heated for the combustion of the incondensible gas and the stored heat of currently the other air heater is transferred to a mixture consisting of carrier gas and the fuel which is to be degasified. This process is also not suited to the carbonization of oil shale and similar carbonizable fuels which are high in inerts, since the fixed carbon material cannot be utilized and, in essence, because the air heaters are heated with incondensible gas. Moreover, the carbonized residue is removed at the carbonization temperature so that the heat losses are also appreciable.