Environmental protection through an exclusion or reduction of pollutant emissions as well as the preservation of resources and an efficient use of energy constitute great challenges of our era.
By the provision of well-proven, efficient and ecologically clean technologies ENVIROTHERM is paying its contribution to the preservation of environment und resources.
This involves the generation of “green” energy, the environmentally acceptable disposal of residues and waste as well as the use of highly efficient flue gas cleaning techniques and the generation of synthetic and fuel gas from solid fuels.
In this respect, the development of high and state-of-art standards is as self-evident as is the use of the latest engineering software. Cooperation with partners, among them university-related ones, allows for a well-directed further development of our technologies.
Gas generation technologies
ENVIROTHERM offers two technologies basing upon the use of solid fuels which can be selected in dependence of the feedstock, the product to be generated and the size of the plant.
The pressurized fixed-bed slagging gasifier designed by British Gas and Lurgi (BGL) is especially applied for large-scale coal-based gas generation plants. The process results in the generation of a high-quality syngas to be used as a basis for various products such as methanol, fertilizers, and electrical power or Fischer-Tropsch fuels.
Gas generation on the basis of a circulating fluidized bed is preferentially applied for the generation of lean and fuel gas from coal and/or biomass.
The principle of a slagging fixed-bed gasifier basing upon the British Gas/Lurgi (BGL) technology is predominantly applied for the generation of high-quality syngas which is free of any attendant substances and can be processed to various products.
The gasifier is operated under a pressure of 30 – 40 bar. Technical oxygen and steam are used as the gasifying medium. Apart from carbon monoxide and hydrogen, the generated syngas contains methane which amounts to 6 - 10 %. With BGL technology, ash turns up as non-leachable slag and, thus, will be at disposal for further utilization (road construction).
The capacity of a standard module (inner diameter of 3.6 m) comes to app. 50 tons per hour. Proceeding from this input appr. 70,000 SCM of syngas will be generated which corresponds to a possible electrical power of 140 - 150 MWel.
The first plant started its operations in the year 2000 in Eastern Germany at Schwarze Pumpe Industrial Park. A mixture of various secondary fuel materials and coal were used as feedstock.
At present, 14 BGL gasifiers have been contracted within the scope of several projects in China and India out of which three have already been put into operation. The other ones are in different stages of project implementation. As an example, a more detailed description is given for the plant situated in Hulunbeier, Inner Mongolia in the References section. The envisaged input materials range from dried briquetted lignite to low-agglomerating hard coal. These materials are used to produce basic materials for the fertilizer industry or to produce gas as a substitute for natural gas.
Gas generation based upon the principle of a circulating fluidized bed of coal, biomass or residues under nearly atmospheric pressure conditions represents a cost-efficient and robust gasification technology.
It is mainly used for the generation of fuel and lean gas. As an example, applications in the cement and steel industry may be mentioned where the produced gas is used as a substitute for other fuel materials such as fuel gas or natural gas.
Other consumers use the non-cleaned gas for direct injection as fuel gas within the cement production process or for combustion in downstream units.
The use of biomass can allow for the achievement of a CO₂-neutral or even a CO₂-positive balance.
Interesting examples concerning this technology may be found in the References section.
ENVIROTHERM Envirotherm can provide the following combustion technologies to ensure both an efficient power generation from solid fuels, sludge or biomass and a safe disposal of hazardous waste materials:
- Stationary fluidized bed for the thermal disposal of industrial and sewage sludge.
- Circulating fluidized bed for power generation from coal, biomass and residues at power stations.
- Incinerators for liquid residues.
- Rotary kiln incineration of liquid, pasty-like or gaseous hazardous waste materials.
- Bogie hearth kiln incineration to dispose of high toxicity residues, e.g. from chemical weapons disposal processes.
Proper flue gas cleaning systems are used to comply with or go below respective emission limits.
For decades clarification of municipal or industrial waste water to meet increasingly stringent purity standards has become a common and mandatory task. During this period of time the sewage sludge which occurs in this sphere turned from a fertilizer earlier considered a natural one into an "unpopular residue" because
- the use of sewage sludge for agricultural purposes was inhibited to a large extent due to legal provisions and will be fully prohibited in the near future.
- in most cases no sufficient dumping areas are at disposal or fit to be approved by local authorities.
These are the reasons why new disposal alternatives had to be found to handle these residual materials. One of those alternatives is provided by the incineration of sludge at temperatures of 850 °C and above in conjunction with a simultaneous utilization of ist energy contents. In this context, the stationary fluidized bed technology proved ist value and became widely accepted. The vast majority of modern incineration plants are equipped with stationary fluidized bed incinerators. They are characterized by the feature of a very efficient heat and individually fitted flue gas cleaning system (dry type, quasi-dry or wet type) compliance with stringent legal provisions is given.
ENVIROTHERM offers fluidized bed technologies designed for the disposal of industrial and municipal (sewage) sludge earlier developed by both companies LURGI and Bamag. Both technologies represent proven and environmentally friendly thermal waste utilization options individually tailored to cope with specific sludge characteristics and provide a high degree of waste disposal security to plant operators. In addition to this, pursuing monoincineration of sludge those operators turn out to be an ideal basis for future activities in the field of phosphorus recovery from produced ashes.
Further development of incineration plants reached a point where, apart from their primary function as sludge disposal units, they are used for electrical power generation and/or district heating purposes without neglecting operational security in this respect. As a rule, those plants can be operated autonomously without external energy supply and, in addition to this, feed electrical energy and/or heat into public or operator's utility networks.
A plant designed to ensure a thermal utilization of sewage sludge basically comprise the following process stages shown in the diagram below:
- Dewatering / preliminary drying.
- Incineration within a fluidized bed.
- Generation of energy (electricity, thermal heat).
- Wastewater cleaning.
- Flue gas cleaning.
Combustion within a circulating atmospheric fluidized bed (CFB) has proved its efficiency for many years and distinguishes itself by both flexibility with respect to feedstock and a high level of environmental acceptability. Thanks to the additional feed of lime stone, sulphur dioxide produced during the combustion process is absorbed to a degree of 90 % yet in the combustion chamber. Gypsum produced in this process is subject to disposal together with the ash. The formation of thermal nitrogen oxides is largely excluded due to the moderate combustion temperature and a staged combustion air feeding mode. CFB allows for a high degree of material and thermal transformation processes at a steady and constant combustion temperature of app. 850 °C.
During recent years ENVIROTHERM, apart from performing the design of coal-fired CFB power stations, has rendered specific support to power station operating companies, particularly, by conducting research studies concerning the extension of fuel feedstock ranges by envisaging an additional feed of fuel substitutes, biomass and sewage sludge. In this course, particular restructuring measures were proposed which, afterwards, were respectively implemented by operating companies.
In this context, the following activities need to be mentioned:
- Change of design of an existing pressurized fluidized bed in order to eliminate process bottlenecks which permitted a significant improvement of plant availability and full-load features.
- Adaption of control systems to modern control concepts and revamping of individual items of equipment.
- Extensive research studies concerning an additional feed of up to 40 % of biomass at a large CFB power plant (100 MWel).
In addition to CFB technology ENVIROTHERM also provides the classic stationary fluidized bed technology.
In many industrial sectors solid, pasty-like, liquid as well as gaseous residues are produced which require an additional treatment. A thermal kind of treatment is frequently chosen nowadays in those cases when the residues have a high calorific value allowing, thus, their use for the generation of energy. In this respect, the rotary kiln technology is mainly applied which, in conjunction with a downstream post-combustion chamber, heat recovery and appropriate flue gas cleaning procedures, provides a low-emission and, thus, an environmentally acceptable hazardous waste disposal option.
Another option for the disposal of particularly liquid or gaseous waste materials is suggested by incineration within a vertically or horizontally arranged combustion chamber. Downstream waste-heat boilers are designed to provide an optimum use of the heat from flue gas prior to its cleaning in accordance with highest standards and release into the atmosphere (the plant located in Izmit is described as an example in the References section). Currently, ENVIROTHERM dealt with the revamp of a rotary kiln system in Siberia designed for the disposal of residues produced at a refinery facility.
A bogie hearth kiln is applied to meet specific process requirements involving simple and failure-free operation of systems.
Under the conditions of an external heat supply by burners and a sufficient holding time waste is routed into the kiln in a batch-wise mode, thermally destroyed at high temperatures or brought to a state allowing a further reduction of pollutant contents by a treatment within the limits of the flue gas flow (post-combustion with downstream flue gas cleaning).
This way, pollutants will be removed from the flue gas flow, subsequently concentrated and disposed of in a safe way. After leaving the bogie hearth kiln the burned out components (ash) will be cooled down and routed to disposal either.
This technology was successfully applied at three plants designed for the disposal of residues from chemical weapons destruction processes within the scope of German disarmament support rendered to Russia.