The core of an incineration plant is the incinerating furnace, the workmanship and capacity is designed according to the estimated quantity and character of the wastes. All the incinerating units are designed as two-stage installations where stage one provides for the maximum burn-up of the material to be incinerated and stage two, so called reactor, provide for parameters of combustion-process flue gas burning up to be up to the legal requirements, which are determined by a minimum stipulated temperature and the flue gas holding period in the end-burning mode. SMS incineration furnaces are designed in away providing for the parameters being met with a sufficient allowance.
Special and extraordinary attention is focused on thermal insulation and refractory materials. They are designed separately with a view to the order and typically, they are sandwich-arranged. The insulation layer composition is designed with regard to mechanical and chemical stress produced on the internal surfaces and at the same time it provided for the required thermal resistance and thermal expansion.
Rotary furnaces excel in universal characteristics in terms of physical properties of the waste to be burnt up and the best efficiency of the waste thermal destruction. Disadvantageous are the higher investment and operating demands. The time of waste passage through the furnace is determined by the degree of the furnace lengthwise axis slope and the rotation rate.
A standard continuous method of inserting the waste using a screw conveyer is employed thus providing for the best possible stabilisation of the chosen thermal mode. It is also a precondition of the enhanced optimisation of the incineration process and the flue gas cleaning.
The end-burning chamber is typically a cylinder set on the base with the burners located tangentially or a multi-flue end- burning chamber with integrated cylinder-shaped reactor and a burner located on its front. The flue gas enters the reactor tangentially. The precondition being met, the wastes with the highest concentration of hazardous substances may be processed.
The chamber furnaces feature lower investments demands, which is an advantage. However, usability of the installations is limited to a degree as combustion of liquid and pasty wastes incineration is limited. The oxidation combustion principle provides for continuous operation of these furnaces, which produced a favourable effect on efficiency of the operation.
Muffle chambers are used in special cases for burning large object, such as varnishing plants grids. However, they may be advantageous for use when liquid wastes are to be disposed of; they are injected then using special jets.
De-ashing of the furnaces is mostly performed in a dry method when the ashes simply fall out into special containers via a dust-tight tube. This principle is also employed for finer-grain sizes of ashes removal from heat cyclones or dust filter.
The heat extraction is designed employer standard processes using a waste heat boiler. The boiler capacity is directly dependent on the heat output of the incineration unit; the output medium and the parameters thereof are then designed with a view to the conditions of further utilisation.
An integrated component of the process may be a facility providing for use of the extracted energy.
The first stage of flue gas cleaning is interception of solid particles borne by the air stream. Regarding the rotary furnaces incinerators, this occurs in the end-burning chamber and afterwards in the heat cyclone that directly follows.
As a standard, a dust filter is used in the process, the type and capacity of which is in conformity with the project. The remains of the finest dust particles are absorbed in the following process of chemical flue gas cleaning.
Flue gas chemical cleaning may be designed as a three-stage absorption process using NaOH as the absorbent active component. Separate stages of absorption are operated at different absorbent pH value and are completely separated at either side. Various types of hazardous substances are separated on a selective basis.
The first absorption stage is formed by a Venturi tube made of titan-containing material. The flues gases are cooled down to the saturation temperature in it, the remaining dust particles are trapped and halogenated compounds and heavy metals are separated.
The other stages are designed in form of sprinkling column, the number and dimension of which is subject to the required efficiency. At these stages, the remaining halogenated compounds are trapped and the acidic compounds of the flue gases are separated. Also a dioxin filter may be included in the line.
An integrated part of the line is peripheral equipment to prepare the absorbing agent and to process saturated absorbing agent by precipitation and filtration. The resulting product of the process is sludge possible to be dug, which is further handled as a hazardous waste, and chemically pure water, partially returned in the process.
NEUTREC method is a modern and very efficient process of flue gases cleaning that is categorised as a so-called dry process. The method was proven in domestic conditions incinerating common health care wastes and the results confirmed the parameters declared by the manufacture of the active substance: finely ground sodium hydrocarbon. In view of investor's and user's aspects, following should be emphasised:
- A high efficiency of the flue gases acidic compounds and heavy metals capture. A dioxin filter is used to intercept any increased contents of organic substances of the furan and dioxin type. The values measured in reference incinerating installations meet the EU 67/86 emission limits with an allowance.
- Very small demands as to the operation.
- Unlike with commonly used processes, the investment and operating costs are significantly lower.
- Simple applicability to existing incineration plants.
SOLVAY company's process contribution in waste incineration is remarkable as it enables a significant reduction of the new project investment costs and consequently, that will shorten the return in a most noticeable way. At the same time, it enables emission limits problems solution in obsolete processes and their service life extension in a very reasonable way.
Dioxin absorption using a dioxin filter is currently a separate issue. Within its own development programme, the company has performed a number of comparison measurement recently to follow the efficiency of various active substances under various conditions and obtained a solution that is on the current European level.
Measurement and control of the entire process in the incineration plant is provided by a master control system - computer. The combustion temperature and flue gases continuous measurement and recording at the phases critical for the preset mode of combustion control and the system underpressure values are performed in a standard manner. O2 and CO concentration in the flue gas is also measured.
According individual instructions, it is possible to monitor and record yet other chemical and physical values.
The measurement and control system offers a possibility to set up the best possible mode of the combustion process in terms of reaching the incineration plant maximum output while the combustion quality criteria are controlled to match the specific kind of waste.