Abstract:
Sewage sludge from municipal and industrial sewage systems can be incinerated in conjunction with the incineration of refuse in a refuse incinerator as environmentally safely as possible, with a favorable energy balance and low expenditures for technology and equipment. The sewage sludge can be fed into a rotary tubular kiln, while in a countercurrent, flue gas from a refuse incinerator can be passed through the rotary tubular kiln. The resulting vapors from the sewage sludge incineration can then be injected back into the refuse incinerator for afterburning, while the components of the vapors are useful for the reduction of the formation of nitrogen oxide during the incineration of the refuse.

Description:
This application is a Continuation-In-Part application of International Application No. PCT/DE92/00531, filed on Jun. 26, 1992, which claims priority from Federal Republic of Germany Patent Application No. P 41 21 968.6, filed on Jun. 28, 1991. International Application No. PCT/DE92/00531 was pending as of the filing date of U.S. application Ser. No. 08/024,161 and the U.S. was an elected state in International Application No. PCT/DE92/00531. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a process for the incineration of sewage sludge and refuse. Sewage sludge from municipal or industrial sewage systems is preferably desiccated and then incinerated in conjunction with a refuse incinerator. 
     2. Background Information 
     Known processes for the harmless disposal of sewage sludge attempt to solve sewage disposal problems by means of drying the sludge and then incinerating the sludge. For example, German Laid Open Patent Application No. 35 42 004 discloses a process for drying sewage sludge with heated exhaust from a clinker cooling system during the manufacture of cement clinker. The process disclosed is specifically tailored to cement production. In addition, the sewage sludge, dried in a separate process stage, is fed as fuel into the sintering furnace. 
     Another example of a disposal process can be found in German Patent No. 36 35 068, which discloses a process for the detoxification of contaminated material as part of a degasification process which includes indirect heating. In this process, whereby the degasification stage involves indirect heating, the drying and incineration of contaminated material do not occur in the same process stage. 
     German Laid Open Patent Appln. No. 39 10 215 discloses a process for the drying and incineration of sewage sludge at a coal-fired power plant. Here, too, drying and incineration do not occur in the same process stage. The vapors are incinerated in the zone where the firing takes place and the dried sludge is added to the coal to be burned. Drying takes place indirectly using condensing steam. The vapors from the drying of the sewage sludge increase the flue gas volume during the burning of the coal. 
     Thus, a process in which the drying, carbonization and incineration of sewage sludge occur in one single process stage is not known. Further, it has been found that such a unified sewage treatment process can be suitable for the formation of reduction agents that are generally necessary for the removal of nitrogen which forms during refuse incineration. It is this combination of sewage treatment and refuse incineration that accounts for the success of the process according to the present invention. 
     OBJECT OF THE INVENTION 
     The object of the invention is to develop a process whereby sewage sludge from municipal and industrial sewage systems can be incinerated in combination with the incineration of refuse in a refuse incinerator in a manner which is as environmentally safe as possible, has a favorable energy balance, and also does not require a great expense for technology and equipment. 
     SUMMARY OF THE INVENTION 
     As discussed briefly above, it has been found that a single process stage for the drying, carbonization and incineration of sewage sludge can produce reduction agents in the exhaust vapors produced thereby, which reduction agents are usable for reducing nitrogen produced upon the incineration of refuse. Thus, conducting the exhaust from a sewage incineration stage to a refuse incinerator can be useful for providing reduction agents for the refuse incineration. Further, the heated exhaust gases from the refuse incineration can be used for the incineration and drying of the sewage sludge. Thus, a simple arrangement in which the exhaust from each of the sewage incineration and the refuse incineration are fed to the other can provide an efficient and environmentally safe waste treatment process. 
     To achieve this, the present invention teaches that sewage sludge, which can be partly desiccated to have a dry material content of about 20% to about 30%, can be fed into a rotary tubular kiln. In a countercurrent to the direction of flow of the sewage sludge through the kiln, flue gas, preferably at a temperature between about 600° C. to about 900° C., can be drawn from a refuse incinerator through the rotary tubular kiln. This feeding of the flue gas from the refuse incineration back through the rotary tubular kiln for incinerating sewage sludge both promotes firing in the rotary tubular kiln, and also allows the sewage sludge to be dried, carbonized and incinerated in preferably a single process stage. Such a single process stage utilizing the heat from the flue gas of refuse incineration can even be performed without necessarily requiring any additional external energy. 
     Further, in such a process as described above, vapors having a high proportion of uncombusted inorganic and organic gases, such as ammonia (NH 3 ), are formed in the rotary tubular kiln during the treatment of the sewage sludge. These vapors, in turn, can be injected back into a refuse incinerator for afterburning of the vapors. In the refuse incinerator, the uncombusted gases also can serve to reduce the formation of nitrogen oxides which can be produced during the incineration of refuse. The operation of the refuse incinerator is only slightly disrupted by such a recycling of exhaust gases because the heat removed to the sewage incineration in the form of hot gases is essentially returned to the refuse incinerator in the form of sensible heat and uncombusted gases having high calorific values. 
     By means of the process according to the present invention in which the exhaust from each of the refuse and sewage sludge incinerators is fed to the other incinerator, refuse/sludge wastes with combined calorific values of up to about 7000 kJ/kg can be incinerated without necessarily requiring any additional energy beyond that used by the refuse incinerator. This would essentially not be possible without the use of additional energy if the individual components were mixed and incinerated in the same furnace. Existing refuse incinerators can even be retrofitted for this process without requiring extensive modification of the sequential incineration stages, such as boiler, filter, exhaust scrubbers, head of the chimney, etc., because the amount of flue gas from refuse incineration does not increase for a constant throughput of refuse. Because the amount of flue gas remains the same, the absolute emissions load of the entire system is less than the emissions load from the incineration of the individual components in separate systems. In addition, the formation of nitrogen oxide in the refuse incinerator can also be reduced by means of the process according to the invention, since the gases produced in the carbonization and drying zones of the sewage sludge rotary tubular kiln, that is, primarily NH 3 , essentially act as reduction agents. 
     One aspect of the invention resides broadly in a process for the incinerating sewage sludge in an incineration apparatus. The process comprises the steps of: conducting sewage sludge to the incineration apparatus, the incineration apparatus having a loading end, a discharge end, and an incineration chamber therebetween; loading sewage sludge into the loading end of the incineration apparatus; combusting the sewage sludge in the incineration chamber to produce combusted sewage sludge and exhaust; at least partially heating the sewage sludge with heated flue gas from a refuse incinerator to provide at least a portion of the heat for the combustion of the sewage sludge; and removing the combusted sewage sludge from the discharge end of the incineration apparatus. 
     Another aspect of the invention resides broadly in a process for conjunctively incinerating refuse and sewage sludge in an incineration device. The incineration device comprises a first incineration apparatus for incinerating the sewage sludge and second incinerating apparatus for incinerating the refuse. The process comprises the steps of: conducting sewage sludge to the first incineration apparatus, the first incineration apparatus having a loading end, a discharge end, and an incineration chamber therebetween; loading the sewage sludge into the loading end of the first incineration apparatus; incinerating the sewage sludge in the incineration chamber of the first incineration apparatus to produce incinerated sewage sludge and exhaust gases; conducting refuse to the second incineration apparatus, the second incineration apparatus having a loading end, a discharge end, and an incineration chamber therebetween; loading the refuse into the loading end of the second incineration apparatus; incinerating the refuse in the incineration chamber of the second incineration apparatus to produce incinerated refuse and heated flue gas; conducting at least a portion of the heated flue gas from the second incineration apparatus to the first incineration apparatus to provide at least a portion of the heat for the combustion of the sewage sludge; removing the combusted sewage sludge from the discharge end of the first incineration apparatus; and conducting the exhaust gases from the first incineration apparatus to the second incineration apparatus to combust the exhaust gases from the first incineration apparatus. 
     Another aspect of the invention resides broadly an apparatus for conjunctively incinerating refuse and sewage sludge. The apparatus comprises a first incineration apparatus for incinerating the sewage sludge, the first incineration apparatus comprising a loading end for loading sewage sludge into the first incineration apparatus, an incineration chamber for incinerating sewage sludge to form incinerated sewage sludge and exhaust gases, and a discharge end for removing incinerated sewage sludge from the first incineration apparatus; a second incineration apparatus for incinerating refuse, the second incineration apparatus comprising, a loading end for loading refuse into the first incineration apparatus, an incineration chamber for incinerating refuse to form incinerated refuse and heated flue gas, and a discharge end for discharging incinerated refuse from the second incineration apparatus; apparatus for conducting at least a portion of the heated flue gas from the second incineration apparatus to the first incineration apparatus to provide at least a portion of the heat for the incineration of the sewage sludge; and apparatus for conducting the exhaust gases from the first incineration apparatus to the second incineration apparatus to combust the exhaust gases from the first incineration apparatus and react reducing agents in the exhaust gases with nitrogen oxides in the flue gas. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The process according to the invention is explained in greater detail below, with reference to the accompanying schematic illustrations, in which: 
     FIG. 1 shows a rotary tubular kiln for sewage sludge combustion in combination with a refuse incinerator for combustion of refuse; and 
     FIG. 2 shows an enlarged detail of a rotary tubular kiln. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows one arrangement, according to the present invention, of a rotary tubular kiln 1 in combination with a refuse incinerator 2. In such a system, sewage sludge 4 is preferably fed first into a mechanical dessicator, or dehydrator 3 by means of pump 4a. Such a dehydrator, or dessicator 3 can be of a type known in the art. In the dessicator 3, the sewage sludge can preferably be at least partially desiccated to have a dry substance content between about 20% to about 30%, however, sludges having dry substance contents outside of this range are also feasibly usable in the incineration process according to the present invention. For example, sludges with dry substance contents of between about 5% to about 20% and about 30% to about 50% may also be usable, but may result in decreased efficiency. Such a dessicating system can also have return piping 5 which could possibly, by means of pump 5a, be used for transporting the water removed from the sewage sludge, or possibly for redirecting sewage sludge having too high of a moisture content back to a sludge storage area for return to the dehydrating stage. 
     The partially dried sewage sludge from the dessicator 3 can then be transferred to a rotary tubular kiln 1 for incineration of the sewage sludge. While a rotary tubular kiln 1 is the preferred apparatus for incineration of the sewage sludge according to the present invention, other types of incinerator apparatus known in the art may also be usable in such an arrangement. As the sewage sludge is passed through the rotary kiln 1, a countercurrent of flue gas 7, preferably at a temperature of between about 600 degrees C. to about 900 degrees C. is drawn from the refuse incinerator 2 through the rotary tubular kiln 1. If necessary, additional combustion air 10 can be vented into the rotary tubular kiln 1 by means of blower 10a to provide a proper firing within the kiln. 
     With reference to FIG. 2, the flue gas is preferably introduced in a combustion and flame zone (A) of the rotary tubular kiln 1 and then preferably flows over the gasification and degasification zone, or carbonization zone (B) to the drying zone (C). In passing from the combustion zone to the drying zone, the flue gas is gradually and continuously cooled. Thus, the sewage sludge is essentially first dried in the drying zone (C) by flue gas at a temperature which might be in a range of between about 200° C. to about 300° C. The dried sewage sludge then passes to carbonization zone (B) where the sludge can be carbonized by flue gas which might be at a temperature within a range of about 300° C. to about 600° C. Lastly, the carbonized, degassified sewage sludge can then pass into the incineration zone (A) where the sewage sludge can be incinerated in the presence of the flue gas having a temperature in a range of about 600° C. to about 900° C. These temperature ranges are only approximations, and such ranges could extend to greater or lower temperatures depending on the operating conditions. 
     At temperatures between about 700 degrees C. to about 300 degrees C., and at oxygen contents below about 5% by volume (wet) behind the flame front, pyrolysis gases and highly volatile gases can be released from the flue gas. This can result in a high proportion of uncombusted gases in the vapors 8, which vapors can preferably be cycled to the refuse incinerator 2, by means of blower 8a, for afterburning of the vapors 8. In addition to ammonia, which is formed primarily in the drying zone (C), other inorganic and organic gases can be formed in the kiln 1, which gases also can be used to reduce the formation of nitrogen oxide during the incineration of the refuse. With a refuse/sludge ratio of 4 (sludge: approximately 100% dry material), nitrogen oxide values of 100 mg/Nm 3  based on 11% O 2  can be achieved. 
     The vapors 8 formed during the sludge incineration in the rotary tubular kiln 1 can preferably be injected back into a refuse incinerator 2, and preferably into a firing, or incineration chamber 11 of the refuse incinerator. Any of various known types of refuse incinerators could be used for carrying out the process according to the present invention. The vapors 8 can be further incinerated in the firing chamber 11 of the incinerator 2. Normal operation of the refuse incinerator 2 may only be slightly disrupted by the injection of the vapors 8 because the heat removed from the refuse incinerator 2 in the form of hot gases is essentially returned to the refuse incinerator in the form of sensible heat, gases with high calorific values, and uncombusted gases. Any exhaust gases not withdrawn from the refuse incinerator to the rotary tubular kiln can essentially be fed through a system of filters and exhaust scrubbers 12 for removal of any additional environmental pollutants, before releasing the exhaust into the atmosphere. 
     The incinerated sewage sludge formed in the rotary tubular kiln can essentially be discharged from the kiln in the form of slag 9, which can be either placed in a landfill or made available for other applications. 
     One feature of the invention resides broadly in the process for the combined incineration of sewage sludge and refuse, characterized by the fact that 
     a) the sewage sludge 4, which has been partly desiccated to 20 to 30% dry material content, is fed into a rotary tubular kiln 1, 
     b) to promote firing, flue gas 7 at a temperature of 600 to 900 degrees C. is drawn from a refuse incinerator 2 through the rotary tubular kiln in a countercurrent, 
     c) the resulting vapors 8, which contain a high proportion of uncombusted inorganic and organic gases, as well as ammonia, are injected into the refuse incinerator 2 for afterburning, 
     d) formation of nitrogen oxide during the incineration of refuse is thereby reduced. 
     Another feature of the invention resides broadly in the process, characterized by the fact that the drying, carbonization and incineration of the partly desiccated sewage sludge in the rotary tubular kiln 1 take place in a single process stage. 
     Yet another feature of the invention resides broadly in the process, characterized by the fact that the drying, carbonization and incineration of the partly desiccated sewage sludge take place in a rotary tubular kiln 1 without additional external energy. 
     Various apparatuses and processes for dehydrating and incinerating sewage sludge which could possibly be used in the context of the present invention are more fully disclosed in the following U.S. Patents: U.S. Pat. No. 5,057,009 to Nechvatal and Heian, entitled &#34;Lightweight Aggregate from Flyash and Sewage Sludge&#34;; U.S. Pat. No. 4,949,654 to Wilson Porter, entitled &#34;Incinerator for Combusting Sewage&#34;; U.S. Pat. No. 3,913,500 to James Paccione and David Omeara, entitled &#34;Heat Treatment of Waste Sludges&#34;; U.S. Pat. No. 3,954,069 to Per Loken, entitled &#34;Process and Apparatus for the Incineration of Aqueous Sewage Sludge&#34;; U.S. Pat. No. 4,050,900 to Jim Hobbs and Craig Smyser, entitled &#34;Incineration Apparatus&#34;; U.S. Pat. No. 4,196,077 to Berkowitz et al., entitled &#34;Sewage Sludge Dewatering&#34;; U.S. Pat. No. 4,202,282 to Jim Hobbs and Craig Smyser, entitled &#34;Method of Incineration&#34;; U.S. Pat. No. 4,311,103 to Yasuo Hirose, entitled &#34;Incineration System for Sewage Sludge&#34;; and U.S. Pat. No. 4,906,388 to Frank Cain and Lawrence Gasper, entitled &#34;Sewage Sludge Dewatering Process&#34;. 
     Various apparatuses and processes for incinerating refuse which could possibly be used in the context of the present invention are more fully disclosed in the following U.S. Patents: U.S. Pat. No. 4,006,693 to Hans Kunstler, entitled &#34;Combustion Furnace Construction Particularly a Refuse Incinerator&#34;; U.S. Pat. No. 4,516,511 to Tsung Kuo, entitled &#34;Refuse Incineration Apparatus&#34;; U.S. Pat. No. 4,706,560 to Gaetano Capodicasa, entitled &#34;Refuse Treatment Apparatus&#34;; U.S. Pat. No. 4,936,231 to Loyd Johnson, entitled &#34;Solid Waste Garbage Incineration System&#34;; U.S. Pat. No. 4,949,653 to James Rast, entitled &#34;Process and Apparatus for Incineration&#34;; and U.S. Pat. No. 5,009,173 to Sedat Temelli, entitled Apparatus for Incineration of Refuse. 
     Similarly, various apparatuses and process for cleaning of the flue gases which could possibly be used in the context of the present invention are more fully disclosed in the following U.S. Patents: U.S. Pat. No. 5,018,457 to Brady et al., entitled &#34;Waste Treatment System&#34;; U.S. Pat. No. 5,050,508 to Paul Wilson, entitled &#34;System for the Incineration of Refuse and the Treatment of the Incineration Exhaust Gasses&#34;; and U.S. Pat. No. 5,127,347 to Eric Cheetham, entitled &#34;Method and Apparatus for the Reduction of Solid Waste Material Using Coherent Radiation&#34;. And filter arrangements can be found in the following U.S. Patent: U.S. Pat. No. 4,416,674 to McMahon et al., entitled &#34;Filter for Treating a Particle-Carrying Gaseous Stream&#34;; U.S. Pat. No.: 4,862,813 to Levin et al., entitled &#34;High Temperature Gas Cleaning in Municipal Solid Waste Incineration Systems&#34;; U.S. Pat. No.: 4,971,769 to Hans Haerle, entitled &#34;Filter Device of use in Heating or Incineration Plants&#34;. 
     All, or substantially all, of the components and methods of the various embodiments may be used with at least one embodiment or all of the embodiments, if any, described herein. 
     All of the patents, patent applications and publications recited herein, if any, are hereby incorporated by reference as if set forth in their entirety herein. 
     The details in the patents, patent applications and publications may be considered to be incorporable, at applicant&#39;s option, into the claims during prosecution as further limitations in the claims to patentably distinguish any amended claims from any applied prior art. 
     The appended drawings, in their entirety, including all dimensions, proportions and/or shapes in at least one embodiment of the invention, are, if applicable, accurate and to scale and are hereby incorporated by reference into this specification. 
     The invention as described hereinabove in the context of the preferred embodiments is not to be taken as limited to all of the provided details thereof, since modifications and variations thereof may be made without departing from the spirit and scope of the invention.