Large-Scale Complex Processing of Solid Carbonaceous Industrial and Domestic Wastes

A.G.Melnichenko

"Coke and chemistry" Number 5 2001.allerton press,inc.//New York

       The problem of solid industrial and household wastes is one of the most urgent and difficultly solvable present-day problems because of the enormous and ever increasing quantities of wastes and a large diversity of their properties. Unless this problem is solved in the first decade of the 21st century, the consequences may become catastrophic.
       The problem is very critical in Ukraine, especially in the., thickly populated industrial Donbass. Since industrial and domestic wastes are not processed on a large scale, the fertile land is used as dumping ground (today more than 30,000 ha out of 170,000 in Ukraine), this being responsible for the ever increasing pollution of water bodies and air with toxic substances.
       The complex scientific and engineering problems that are to be solved are, in our opinion, weighty factors hindering the development of efficient methods and equipment for the processing of solid wastes. This is largely associated with the instability of the feedstock base. The physico-mechanical properties of the majority of solid industrial and domestic wastes and the regularities of the change of their properties have been studied little. The existing information is incomplete and has not been systematized. The development of the equipment for the processing of such materials is objectively a very complicated task. No large plants have been built so far for the complex processing of industrial and domestic wastes. Very limited amounts of neutral or slightly toxic wastes are selectively processed, which is why the ecological effect of such processing is insignificant.
       The well-known technologies of combustion or processing of solid wastes are used for some types of wastes and are expensive and imperfect since they give rise to new problems or are not suitable at all for Ukraine for reasons of economical, ecological and social character. It is important that more than half of all types of solid industrial and domestic wastes in Donbass are carbonaceous and contain organic matter, which is the raw material for chemical processing or is used as fuel. The ash components of such wastes can be used in the manufacture of building materials. An even greater amount of organic matter is contained in domestic wastes. However, only one-tenth of the resources of industrial and domestic wastes is used; domestic wastes are used in much smaller quantities.
       The workers of Donetsk Technological University are concerned with the development of the equipment and technology for complex processing of solid carbonaceous wastes (SCW) of industrial and domestic origin on the basis of the processes of thermal degradation and synthesis of the organic matter of wastes in inclined thermolysis furnaces (ITF) with the manufacture of useful products and energy. Laboratory studies of "compound-mixes of solid industrial and domestic wastes have demonstrated wide possibilities of the new technology for the initial composition of the raw material.
       On the basis of the summarizing of the world experience in the processing of solid carbonaceous industrial and domestic wastes and of the analysis of the present-day state and importance of this problem in Ukraine and other countries and of the results of investigations carried out in Donetsk Technological University, the following conceptual considerations were taken into account in the development of the given technology.
       1. The technology is based on the thermolysis of the organic matter of wastes. This is the main stage of processing, which proceeds in sealed chambers of ITF and which is the controlled process of thermal degradation of the raw material with the formation of solid thermolysis fuel and a mixture of volatiles in the form of vapor-gas and liquid hydrocarbon products.
       2. The complex character of processing and compounding of waste mixtures. This implies the joint processing of a wide gamut of mixtures of hydrocarbon industrial and domestic wastes. The solid and liquid components of wastes in various proportions, depending on their physical properties and chemical composition, are mixed at the stage of preparation of the raw material in order to obtain compound mixtures of required quality.
       3. The large scale of industrial installations. The volumes of accumulation and generation of industrial and domestic wastes are so enormous that it becomes necessary to build high-capacity installations and to involve, in the sphere of processing, the infrastructure of industries, primarily byproduct coke plants.
       4. The controllability and flexibility of the process. This is achieved due to the possibility of the joint application of several controlling factors: the temperature regime of thermolysis, the pressure of the preliminary compaction of the raw material, the cyclic charging, the flow velocity of the working mass in installations, etc. Optimal control is effected on the basis of a knowledge of the properties of the feed and of the demands for the products and energy obtained with the use of computers, automation facilities and controlling functions of the personnel.
       5. The high level of technogenic safety. The industrial complex is designed for a higher level of requirements for the sealing of technological apparatuses as compared with those existing in the industry, entrapment and complete decontamination and chemical processing of all thermolysis products. Use should be made of tested technological and designing measures capable of creating prerequisites for efficient environmental protection.
       6. The high degree of utilization of the energy-chemical potential of wastes. This is achieved by the development of a complete cycle of thorough processing of waste mixtures with the manufacture of useful products and energy, namely thermolysis gas, liquid hydrocarbons, solid fuel, electric power and building materials.
       7. The economic efficiency. With relatively low capital costs the process can be made economically profitable due the use of cheap organic materials of various origin with the manufacture of useful products, the protection of soil, water and air from contamination, the elimination of refuse piles, dumps, sludge and slime pits, settling tanks, and also of the infrastructure of byproduct coke plants.
       8. The social effect. The involvement of the personnel and basic facilities of byproduct coke plants, which cut down production and the building of equipment, machines, installations and structure of the industrial complex in the processing of wastes in machine-building and refractory plants contributes to the creation of jobs for the unemployed.

       Fig. 1. Diagram of thermolysis energy block for processing of industrial and domestic wastes: (A) air feeding into burner; (B) flue gases for purification; (C) feeding of gas and air for heating the furnace; (D) feeding of water into boiler unit; (E) steam off take to turbine; (F) withdrawal of chemicals for processing; (1) charging system; (2) pressing-pushing device; (3) thermolysis furnace; (4) furnace heating system; (5) volatiles withdrawal system; (6) sloping flue; (7) burner; (8) boiler unit; (9) ash-removal system.
        The processing technology has the following sequence of basic operations:
       1.the screening and classification of the feed with the extraction of course inclusions of metal, glass and ceramics;
       2.the pulverization, proportioning and mixing of the components
       3.the charging of a mix of solid carbonaceous wastes into the installation and its densification;
       4.the thermolysis of the SCW mixture with the production of a solid thermolysis fuel and volatile chemicals, which are to be processed by conventional methods;
       5.the combustion of the solid thermolysis fuel with the utilization of the heat;
       6.the transfer of ash residues for the manufacture of building materials.

       Fig.2.Schematik representation of material flows in combustion processes A and in thermolysis energy-processing of solid industrial and domestic wastes B.
       The charging of the mixture, its compaction and thermolysis and the combustion of the solid fuel are carried out in a single installation (Fig. 1). The thermolysis process is characterized by high ecological safety since it takes place in a closed space of the sealed chamber, continuity and by efficient control; also, it is automated. The inclined thermolysis furnaces are relatively simple, provide the action of several controlling factors on the feed and are built in batteries. This creates the prerequisites for their reliability,economical efficiency, good thermotechnical characteristics of the installations and possibility of using advanced measures tested in coke production.
       The highly efficient processing of solid carbonaceous wastes by a new method is realizable if the homogeneity of the raw material and the stability of its basic physico-mechanical and technological properties are provided. These properties can be controlled to a certain extent by means of pretreatment and mechanical, chemical and thermal actions, which include pulverization equalizing, proportioning and mixing of the components in certain ratios, the addition of required amounts of liquid binder substances, solid additives, stamping of the charge followed by controlled heat treatment. Many of the advantages of the new method (as compared with the conventional combustion) become evident upon tfieir general analysis (Fig. 2).
       Such a complex processing of wastes seems to be not only the most ecologically safe method among those known to date but also an economically profitable process. The payback period for the industrial complex is 2 years at most. Some of the engineering developments of the project are protected by patents. The practical implementation of the process is planned in some Ukrainian byproduct coke plants.
       The above-described conception and engineering ideas create the basis for the efficient solution of the global problem — the development of the equipment and technology for the large-scale complex processing of solid industrial and municipal wastes with the manufacture of useful chemicals, fuel, energy and building materials with the provision of a high level of technogenic safety.