Abstract:
The invention concerns a process for the storage of heterogeneous wastes in holding or supply dumps, such as rubbish bunkers or suitable rubbish containers, prior to its removal and subsequent thermal utilization or some other processing technique. By introducing a variable flow of inert gas consisting essentially of nitrogen and carbon dioxide into the rubbish bunker, fires and gas explosions are practically excluded, aerobic decomposition processes are suppressed, and anaerobic decomposition is retarded. Using a variable flow of inert gas also prevents the further formation of dioxins and furans in a subsequent thermal utilization, as well as reliably preventing vermin from attacking the rubbish. By avoiding or at least significantly reducing these disturbances in the bunker zone, disposal safety is significantly increased. Storage of the wastes preferably takes place in an essentially inert atmosphere which is introduced into the rubbish bunker adjacent the bottom so that the inert gas flows upwardly through the rubbish. Storage of the wastes in an inert atmosphere essentially prevents the occurrence of a fire.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 08/693,122 filed Oct. 16, 1996, and now abandoned, which in turn, is a 371 of PCT/DE95/00191 file Feb. 15, 1995. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention concerns a process for the storage of heterogenous rubbish in holding or supply dumps such as rubbish bunkers or suitable rubbish containers before its removal and subsequent thermal utilization or a different processing operation. 
     2. Description of Related Art 
     Plants where wastes (such as domestic and special garbage, clearing sludge and industrial scrap) are thermally treated, have rubbish bunkers on the entry side. Relatively large quantities of these heterogeneous waste materials are stored temporarily or as a supply in the rubbish bunkers. These wastes, designated here as a whole using the term “rubbish”, are a significant environmental risk due to their very heterogeneous composition and their usual storage quantities in the thousands of tons. 
     Ignition sources, such as furnace ashes, chemicals and metal parts are brought into the rubbish bunkers uninspected. Aerobic and anaerobic processes also take place in the rubbish bunker, despite the continuous exchange of air, which among other things can cause an increase in temperature to the point of spontaneous combustion. The ignition sources and the aerobic and anaerobic processes which can possibly cause combustion are collectively referred to as “disturbance law.” 
     Rubbish bunkers are therefore a potential danger in the sense of the disturbance law. Disturbances result in considerable and extremely negative effects. Obviously these negative disturbances in the rubbish bunker can lead to other types of disturbances in other areas of the plant with even greater negative effects (J. Look,  TÜV Bayer/Sachsen,  Safety Technology in Rubbish-incineration Plants with a View to the Disturbance Law. Conference on the Thermal Disposal of Wastes and Rubbish, Dec. 9-10, 1993, Cologne). 
     The significant hazardous materials released by burning are: heavy-metal compounds; acid gases; organic pollutants from the low-temperature carbonization of plastics; and polyhalogenated dibenzodioxins and furans as well as other carcinogenic materials. 
     The studies from the  TÜV Bayer/Sachsen (Look), cited above, document the potential qualitative and quantitative hazardous-materials in a manageable form. 
     The aerobic and anaerobic processes that take place in the rubbish bunker typically cause the temperature near the center of the rubbish pile to rise. Eventually the temperature can rise to the point of spontaneous combustion leading to smoldering fires which spread long unnoticed beneath the surface of the rubbish and are frequently difficult to reach. These smoldering fires in the bunkers of large plants can therefore persist for a long time, possibly several weeks. 
     The frequency and duration of the rubbish-bunker fires represent not only a considerable ecological risk, but also reduce the availability of the rubbish-incineration plants for other processing purposes and impair the safety of disposal. 
     Aside from the ecological and technical problems which a rubbish bunker fire brings with it, the economic burden is significant. Besides the interruption of operations and the halt to disposal thus associated with it, the partially burned rubbish, soaked with the fire-extinguishing agent, must be removed from the bunker after the fire has been put out along with all pollutants and disposed of elsewhere. The economic, ecological and technical damages borne by the operator of such plants are inadequately covered by insurance. Insurers find it difficult to estimate the risk of bunker fires, thus the already considerable insurance premiums continue to rise. Another factor which contributes to high insurance premiums is the possibility of litigation resulting from damage caused by the fires. 
     A further risk arising from the storage of rubbish in holding or supply dumps is represented by the methane buildup resulting from possible decomposition processes. When methane is mixed with air, an ignitable gas mixture is created which can lead to increased danger of explosion. 
     Measured against the possible expansion of a bunker fire and the dangers involved with the formation of ignitable gas mixtures, a possible attack upon the stored material by pests in the storage area is of course not as dangerous. However, here too, some precautionary measures must be taken. 
     It was and is therefore the concern of the technical world to recognize bunker fires early, to begin application of appropriate extinguishing means at the earliest possible time and to avoid the formation ignitable gas mixtures by intensive air circulation in the rubbish bunkers. The relevant state of the art has thus far been limited to fighting fires in the rubbish bunker only in the event of a blaze. Special precautionary measures for fire prevention are not available at this point. 
     Rubbish bunkers in conformity with the existing fire-protection requirements must, among other things, be equipped with fire walls, heat-resistant extraction devices, shutters on vents for smoke and heat, safety units supplied by emergency electric power, fire-monitoring systems and infrared cameras for possible localization of the site of the fire. Because rubbish-bunker fires are as a rule not on the surface, but develop inside the stored rubbish, the necessary technical means for fire fighting are inadequately suitable, despite infrared cameras, for pinpointing the locality of the fire precisely and fighting it efficiently, and are by no means suitable for preventing it before it arises. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is therefore to create a process in which the fires and gas explosions can be practically prevented during the storage of waste of the type described in bunkers or large containers, aerobic decomposition processes being suppressed and anaerobic decomposition retarded, in which case moreover the formation of dioxins and furans in a subsequent thermal utilization is prevented insofar as possible, and attack of the stored materials by vermin is reliably prevented. By reducing these disturbances in the bunker, the safety of disposal should be reliably increased, and operating costs reduced. 
     The goal of the invention is achieved by a process for storing heterogeneous rubbish in holding or supply containers, such as rubbish bunkers or suitable rubbish containers, before its removal and subsequent thermal utilization or a different processing operation. The invention is characterized by the storing the wastes in an essentially inert atmosphere secure from fire danger. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic view of the inventive process. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     By virtue of the fact that the storage of the rubbish is implemented in an atmosphere of inert gas, with the inert gas flowing through the rubbish, the oxygen necessary for the formation of fires is absent at each point in time and at each storage location. Externally introduced ignition sources are extinguished, a spontaneous combustion of the rubbish, induced by exothermal decomposition processes, is prevented, aerobic decomposition processes do not take place, and anaerobic decomposition is at least slowed with the presence of nitrogen and/or carbon dioxide. Attack of the stored materials by vermin will also fail to take place in an inert atmosphere. 
     If the interior pressure of the inert-gas atmosphere in the rubbish bunker diverges from the external pressure, there will thus be no odor pollution in the bunker vicinity due to the slight pressure difference in the bunker. The inert-gas atmosphere can be shut off from the external air by the use of suitable pressure locks which are located adjacent to the rubbish bunker. 
     Because the inert-gas atmosphere does not permit bunker fires to develop and excludes the formation of ignitable gas mixtures, the currently prescribed frequent changing of the bunker atmosphere becomes superfluous. Thus, when the rubbish bunker containing heterogeneous rubbish in an inert atmosphere is sealed off from external air by the pressure locks, there is no need for replacement of inert gas. Replacement of inert gas is necessary only in the case of the slight loss of inert gas taking place during operation of the loading and discharge locks. It is important for the highest standard of safety that inert gas is passed not only through the bunker, but through the rubbish itself. Arising with this type of operation is the advantage that even the atmospheric oxygen simultaneously introduced in the volume of the rubbish is reliably removed and replaced with inert gas. By arranging the inert-gas feed in the floor zone of the storage bunker, a reliable flow of inert gas through the rubbish can be achieved without difficulty. 
     The rubbish introduced into the inert atmosphere contains ordinarily only small amounts of oxygen. With subsequent degassing during thermal preparation, which occurs during a later stage of the rubbish treatment process, the formation of organic pollutants, for example dioxins and furans, is largely suppressed. 
     In the case of known rubbish-treatment processes, the gasification of the carbon components present in the heterogeneous mixture is carried out with the aid of more or less pure oxygen. This, in a known process as disclosed in U.S. Pat. No. 5,282,931, according to DE-OS 4,130,416, the rubbish is compressed into packets which are pre-heated before being fed into a high temperature reactor. Specifically, the rubbish is first compressed, thermally pretreated in this state with the exclusion of air, and the carbon thus obtained with the aid of oxygen is then gasified. Metallic components in the rubbish can be melted out, nonmetallic components can mineralized to prevent leaching. 
     The waste material to be prepared according to this process is however stored in a rubbish bunker in the presence of oxygen prior to compression. The possibility of combustion occurring in this rubbish bunker, for example, by dragging in glowing ashes or, the like, cannot be prevented in this situation. 
     The oxygen required by the known process in the high-temperature stage, is obtained by air decomposition. The nitrogen thereby occurs as a waste product. The nitrogen required for the inert-gas atmosphere in the storage bunker occurs here in a directly usable form. The inert-gas, impacting of the rubbish with this nitrogen thus produces no supplementary costs; rather, it considerably reduces investment and operating costs. In a likewise favorable manner, the carbon dioxide component can also be employed as an inert-gas atmosphere, to the extent it can be utilized for this purpose in the waste treatment plant. 
     Moreover, the exhaust gases, after thermal utilization of the synthesis gases, contain carbon dioxide which can be separated by conventional methods and used as inert gas for the storage of rubbish, that is, for generation of the inert atmosphere. The heat from the waste treatment system can be used for carbon dioxide separation. 
     If synthesis gas is generated in a thermal treatment of rubbish according to the process cited above, it can contain up to 30% of carbon dioxide which is then separated and employed as inert gas for the storage of rubbish in this inert atmosphere. Here, too, the heat from the plant itself can be employed advantageously for carbon dioxide separation. 
     An application of the invented process is also possible in conventional plants of any other type, because the flue gases of these rubbish-incineration plants contain carbon dioxide which is separated with standard methods and can be used as inert gas for the long-term storage of the wastes in an inert atmosphere, in which case the system heat can also be employed for carbon dioxide separation. 
     Carbon dioxide as the inert gas has the additional advantage that the inert gas extracted from the bunker, from the high-temperature zone, is fed to a thermal treatment plant, decontaminated there and can be optionally included in the gasification process. Extraction of the inert gas from the bunker is through an outlet means of the various types well known in the art. 
     It is in any case advantageous, if the inert-gas atmosphere is monitored for residual gas components, particularly for oxygen residues and methane fractions. Such monitoring is desirable not only in the actual bunker zone, but also in that of the pressure locks. 
     Fire-safe storage of heterogeneous rubbish in an inert gas is to take place inside a container sealed off from the outer world. It is also possible for a plant operated independently of the preparation and/or the processing of the waste to use this storage method. 
     The invented process guarantees the greatest possible availability of the plant in question with correspondingly improved disposal safety. Because it is possible to eliminate active and passive measures for fire protection, significant cost savings can be achieved. Due to the absence 
     A rubbish bunker  10  having a bottom  14  contains heterogeneous rubbish made up of various bulk waste materials  12 , as shown in FIG.  1 . An inert gas from a supply or source  26  enters the bunker  10  via a conical inlet  16  at the perforated bottom  14  of the bunker  10 . A valve  17  controls the flow of inert gas into tile bottom  14  of the bunker  10 . This storage inert gas passes through the heterogeneous waste  12  removing and replacing the undesirable combustible gases with a storage inert gas which prevents combustion from occurring in the rubbish bunker  10 . The waste  12  is loaded and unloaded through locks or compartments  19  and  20  which are next-adjacent to the bunker  10 . The bunker  10  has openings which are opened and closed by doors  21  which are raised and lowered and which are pneumatically sealed when closed to prevent gases from entering or leaving the bunker  10  around the doors  21  therein. Although one lock may be used for both loading and unloading, the embodiment illustrated utilizes two locks  19  and  20 , the first  19  for loading the bunker  10  and the second  20  for unloading tile bunker  10 . 
     As the storage inert gas passes through the waste  12 , the undesirable and/or used gases contained within the waste  12  are extracted via an outlet line  18  and stored in a storage container  28 . Alternatively, these extracted gases can be properly vented to the external atmosphere. Optionally, the storage inert gas can be extracted from the bunker  10 , via the outlet  18 , and fed to a thermal gasification station or plant  22 , via the storage tank  28  and line  29 , or directly, where it cain be used in subsequent waste treatment processes. 
     Minimal amounts of storage inert gas are lost by using the discharge locks  19  and  20  when either of the doors  21  is open. However, the gas atmosphere in the bunker  10  and in the discharge locks  19  and  20  is monitored with monitoring devices  24  to ensure that proper levels of inert gas are maintained a valve  25  controls the extraction of storage inert gas from the bunker  10  by a pump  27  in the line  18 . Also, a pressure gage  23  measures the pressure in the bunker  10  and sends a signal to the source of inert gas  26  to supply the predetermined amount or pressure of inert gas into the bunker  10 . 
     Preferably, the thermal gasification station  22  is spaced from the bunker  10 . The rubbish  12  is loaded from the first lock  19  by a robot  15  in the first lock  19  through the opening controlled by the first door  21  between the first or loading lock  19  and the bunker  10 . The rubbish  12  is unloaded from the bunker  10  to the second or unloading lock  20  by a robot arm  30  in the bunker  10 , the door  21  being open during such a transfer. Thereafter, the rubbish  12  is moved by another robot arm  34  in the lock  20  through a doorway controlled by a door  36  arid through a doorway controlled by a door  38  from the second lock  20  and into the thermal gasification station  22 . The rubbish is gasified in the thermal gasification station  22  into various gases including a by-product inert gas, such as carbon dioxide. All of the robots  15 ,  30  and  34  have pick-up fingers  32  for scooping or grasping the rubbish  12 . 
     The by-product inert gas from the thermal gasification station  22  can be conveyed through a line  40  controlled by a valve  42  back to the source  26  and hence to the to the bottom of the bunker for use as the storage inert gas. Alternatively, the inert gas can be supplied to the source  26  from an independent source. 
     Accordingly, the invention provides a method for storing heterogeneous rubbish  12  made up of various bulk waste materials in a closed rubbish bunker  10  having a bottom  14  and at least one opening  21  which may be opened and closed. The method comprises the steps of loading  15 , storing  10  and unloading  34  rubbish into and out of the bunker  10 . Inherent in the method is the closing and sealing the opening while storing rubbish  12  in the bunker  10 . Also included is the step of introducing a storage inert gas into the bottom  14  of the bunker  10  for flowing the storage inert gas upwardly through the stored rubbish  12  to prevent combustion of the rubbish  12 . All the while, the method continuously controls the flow of storage inert gas through the rubbish  12  while the opening  21  is open for replacing the storage inert gas lost through the opening during loading and unloading of the rubbish to continually prevent combustion of the rubbish in the bunker. The storage inert gas is extracted from the bunker  10  through the line  18  for a continuous flow of storage inert gas through the stored rubbish  12 . 
     The method also includes the step of thermally gasifying the rubbish  12  in a thermal gasification station  22  spaced from the bunker  10  and moving the rubbish  12  unloaded from the bunker to the thermal gasification station  22  for thermally gasifying the rubbish into various gases including a by-product inert gas. The by-product inert gas, e.g., carbon dioxide, from the thermal gasification station  22  is conveyed through the line  40  and valve  42  to the supply  26  and to the bottom  14  of the bunker  10  for use as the storage inert gas. Preferably, either one of carbon dioxide and/or nitrogen is used as the storage inert gas. 
     As alluded to above, the pressure of the storage inert gas in the bunker  10  is maintained at a pressure different than atmosphere pressure surrounding the bunker, preferably at a lower pressure than atmosphere pressure surrounding the bunker. In addition, a monitor  26  monitors the inside of the bunker for gases which would support combustion of the rubbish and sends a signal to the supply  26  for increases the flow of inert gas into the bunker  10 . 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be descriptive rather than limiting. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.