Conversion of waste products into energy Moscow to be on european way of solid domestic waste control

Litun D.C, Ryabov G.A, Russian Heat Engineering Institute, Moscow

Any human life activity is associated to collection of huge amount of different wastes. Last decades, the new jump-growing tendency of consumption leaded to considerable increase of solid domestic waste volumes. Today, the mass of solid domestic waste generated within the biosphere achieved almost geological scale and amounts to about 400 million tons per year. As per estimation made by different analysts, Moscow is the city where the volume of collected solid waste makes up the range of 2 to 3.5 million tons, but only 10% of them are recycled.

Judging by the EC countries consumption waste control experience it may be stated that with economy expansion developed, there the direct relation between the gross domestic product and wastes is appeared. Therefore, in the conditions of continuous economic growth the volume of solid domestic waste daily collected in Moscow is steadily increased. Today, the number of solid waste landfills formed around Moscow makes up 167 polygons including only 58 of authorized ones and 109 of spontaneous ones, while 27 of these polygons are up and 19 – filled by 90%. So, no promising expandability is anticipated for the polygons are about to be out. For example, as per the data specified by Russian Federation Ministry of Natural Resources, all the solid waste polygons that support the southern district of Moscow are about to be over in 2-3 years. In the event of this, any new burying places would be allowed to arrange only beyond the bounds of 100-km zone of Moscow. In the coarse of constantly increasing flow of collected wastes the main task is set for polygon-disposed waste recycling. In a number of industrially developed European countries that were the first ones to face the problem of deficit for the areas to be used for disposal of large city municipal wastes there was applied the new drastic method of thermal neutralization of solid domestic wastes to be converted for the purpose of generation of heat and/or electric energy. The method of waste recycling to be implemented by means of selection and sorting of remains at special waste-processing factories makes it possible to decrease the volume of disposed wastes maximum by 50% (the share to be in future achieved under the conditions of waste-processing plant modernization). The wastes thermally processed or buried are subject to the process technology terminating elements.  Waste incinerating process is used for sanitary and hygienic treatment of any polygon environment and encourages decrease of the waste volumes buried up to 10% of the initial capacity. It should be noted that any domestic waste may be converted to biofuel with its low heat value to be specified per Moscow polygon waste working mass on the average of 7500-8000 kJ/kg, humidity – about 30-40% and ash content – 23-30%. Due to change of its morphological content (increase of package, plastic and paper shares and decrease of food waste), the rate of solid domestic waste temperature is raised (in European countries the very value achieves 10 500 – 12 500 kJ/kg). With the solid domestic waste processed and converted into heat and electric energy generating fuel (as compared to its disposal) the potentialities to save conventional types of fuel (coal, gas, fuel oil) on the one hand and to decrease greenhouse gas atmosphere emission on the other hand may be applied. Some legislative acts to have been adopted in the European countries for the purpose of stimulating of solid domestic waste treatment resulted in expanding of the waste thermal treatment facilities both the constructed and reconstructed ones.

Considering the situation that emerged in Moscow and accounting for the European waste control experience the new concept of Moscow sanitary and hygiene cleaning was approved by the city administration in 1992. The above concept included step-by-step transition to the industrial methods of waste treatment to be held on the bases of the waste-burning and waste-processing plants constructed, as well as operating plants reconstructed. At that time, some historical events had been already held including construction of three special waste-treatment plants (with use of refuse incinerators). The first incinerator plant of 9 t/h total output was commissioned in Moscow in 1972. It was intended for burning of composting remains and was used at waste-processing Factory No.1 (Vagonoremontnaya str.) The incineration shop was located at the same building together with the rest factory shops. Due to imperfection of the composting technological process, as well as for absence of market demand this shop was closed in 1985. The first incinerating factory (Factory No.2) was built in Moscow (north district of Degunino) and included two processing lines delivered by French company “CNIM”. In 1984, to the south of the city (district Biryulyovo), the largest for that time domestic incinerating Factory No. 3 equipped with processing facilities “Volund” (Denmark) was commissioned. Each of its four aggregates had a capacity of 12.5 tons per hour. All the above three factories applied the fuel-bed firing technology that was widely used all over the world.

By the nineties of the last century all the Moscow factories equipment largely became obsolescent. For the first thing, the matter is that the level of harmful substance atmosphere emission did not meet the up-to-date restrictive guidelines regulating the process of solid domestic waste incineration. Due to unavailability of Russian regulations, the EEC legal acts were used. Later, in 1994 the above acts were united upon adopting of unified standards EU 94/67/EEC. In compliance with those standards, the SDW thermal process should meet additional environment protection requirements. The guidelines (see Table 1) specified for factories incinerating solid domestic wastes are more rigorous than the ones specified for thermal power plant operating on fossil fuel.

Table 1 – Solid waste and organic solid fuel incinerating plant gas pollutant emission guidelines

The above parameters relate to the dry gas factors reduced to their standard conditions (temperature – 273K, pressure – 101.3 kPa and concentration of Î₂ – 11%).

1) TEQ – in terms of toxic equivalent 2, 3, 7, 8 – TCDD.

2) For boiler steam capacity – up to 320 t/h.

3) Larger value - for reduced content of ash À_reduced to be more than 2.5%-g/MJ, less value – for À_reduced < 0.6%-g/MJ.

4) Less value - for brown coal firing, less value - for slag drip coal firing.

5) Less value – for reduced content of sulfur S _reduced to be less than 0.045%-kg/MJ, larger value – for S _reduced

Today, the emission control regulations are adopted by Moscow administration as the basic ones and must be followed in case of developing, construction and operation of any solid domestic waste incinerating factories.

In addition to their moral depreciation the Moscow factory facilities were featured with physical one. And, as a result, the rate of real output of factories No. 2 and No. 3 to be compared to the rate of potential output was considerably decreased.

For increasing of solid domestic waste output and for reconstruction of Moscow special-purpose factories, Factory No. 2 was the first one subject to modification. Instead of the old factory, the new power station operating on alternate fuel was built by 2000. As compared to the sold domestic waste treatment factories previously built up in Russia, this one generates heat energy that does not utilized by the municipal heat supply system, but converted into electric energy, one part of which is used for covering of own costs and another part is delivered for municipal needs. Today, the power station consists of three turbines Ï-12-13/6 manufactured by Kaluga turbine works and three solid domestic waste thermal treatment energotechnological lines produced by the waste incinerating factory equipment key manufacturer - French company “CNIM”. Each line is fit out with a boiler that can operate in the mode to be applied for decreasing the rate of generation of dioxins, furans and carbon monoxide; dry-type gas cleaning multistage system and industrial control system to be used for plant operation automated control. The method of fuel-bed firing is assimilated at the station. The feeder permanently delivers a certain amount of solid domestic wastes to the furnace equipped with the reverse-pushing grate of “Martin” system. Gas torches are used for firing and for maintaining of the temperature specified (850–930 ºÑ). Under own weight and affected by moving bars the remains are moved from the feeder to the lower section of the inclined fire grate, where the slag-disposal unit is installed. A certain portion of air (primary air) is heated in the steam air preheater and fed from the bottom holes of the fire grate. Secondary air is distributed over the upper layer face for the purpose of afterburning of incomplete combustion products. The furnace gas heat is generated in superheated steam at the exhaust-heat boiler. To minimize formation of dioxins and incomplete combustion products, the furnace gas residence time to be specified at the temperature of more than 850 ºC should make up minimum two seconds with air excess being not less than 1.4. By means of urea being fed in the furnace and reagent mixture (activated carbon with alkali sorbent) injected in the dry-and-wet absorber the concentration of harmful substance content to be available in furnace gas is decreased. As for the final stage the bag filter to be used for filtering of furnace gas from any gaseous agents is installed. The smoke exhauster directs cleaned furnace gas to the chimney. The steam generated and parameterized by (ð = 1.4 MPa, t = 240 ºÑ) is delivered from all the three lines to the common steam main and then to the turbines.

In 2005, upon finishing adjustment works, Moscow special-purpose factory No. 4 (industrial territory “Rudnyovo”) equipped with three technological lines of “Holter ABT” to be used for incinerating of solid domestic waste in vertical fluidized bed was commissioned. Due to the effect created by distributed high-speed air supply, grate shape and combustion chamber profile, the conditions of fluidization of air fuel mixture with two symmetric vortexes (so-called vortex fluidized bed) are produced in the lower part of the furnace plant. Slag is evacuated by means of the layer material external circulation profile consisting of water-cooled discharge screws and vibrating sieve. The treated layer coarse-fraction ash (slag) is discharged out of the plant and fine-fraction ash is delivered to the bypass hopper and returned to the furnace plant by means of horizontal screw. Thus, efficient mixing of layer material, extended residence time of solid waste particles in the furnace, compensation of layer material loss and low temperature (550–700 ºÑ) complete burning carbon is provided. For the purpose of low temperature, the layer air-flow coefficient is always less then a unit, but incomplete combustion products can be burned up at the temperature, to be created within the overlayer zone due to effect of secondary air, of more than 850 ºÑ. As a result of the above two-stage combustion method, the rate of nitric oxides generated and concentrated in furnace gas up to the amount of 200 mg/nm³ (in terms of dry gas and 11% of oxygen) may be decreased. The furnace plant is designed for firing of ground solid domestic waste to have the rate of 13.5 t/h output and operating mass combustion heat - 6500 KJ/kg (maximum size of waste particles – not more than 300 mm). Waste is ground in the pre-treating shop with partial sorting of solid domestic waste and utilization of some secondly used materials (ferrous metal, cardboard, plastic bottles and glass). Thus, special-purpose factory No.4 was the first in Russia, where one of the variants of so-called aggregate technologies combining different methods of solid domestic waste treatment (in this case “recycling-incinerating”) was implemented commercially. These kinds of technologies are intensely adopted in industrially developing countries and may be considered as the most promising ways of solid waste utilization.

Except of the furnace plant, each technological line consists of boiler-utilizer, cyclone, spray absorber, dioxin, furan and mercury catching reagent-feeding unit, bag filter and smoke exhauster arranged behind the furnace plant in sequence as per direction of gas running. The gas analyzer installed at the chimney input automatically registers concentration of main chimney pollutants. On the basis of the HCl and SO₂ concentration the rate of lime pulp supplied to the absorber is regulated. Two turbo-units of 6 MW each (Kaluga Turbine Plant) are used for generation of electric energy.

Two additional solid waste power stations equipped with the up-to-date fire-bed firing facilities will be commissioned in Moscow as soon as possible. Construction of one of the power stations is about to be finished at site of special-purpose Factory No.3. The turnkey construction project is realized by Austrian company “EVN Holding” and implemented with use of own technological lines and steam boilers produced by Podolsk Engineering Plant. The alternate fuel power station that is constructed at site of special-purpose Factory No.1 by Hungarian bidder “Budapro” is just at the point of starting. The main technological equipment will be produced by engineering contract or delivered by one of the incinerating facility producer – Swiss company “Von Roll”.

Moscow waste incinerating thermal power plants commercial operation experience had proved that all the specific facilities can be operated in accordance with the Russian and EC ecological requirements specified for solid domestic waste thermal treatment process. The new alternate fuel power station facilities are able to meet the today requirements and make it possible to solve both the problems of solid domestic waste sanitary purification and city-bordering district power supply. At the same time, there are some problems related to construction of solid domestic waste processing plants. The matter of treatment of all the ash and slag remains and gas purification solid products left upon incineration of solid domestic waste is not resolved yet. The regional power company using its monopolistic market position used to purchase electric energy generated at the special-purpose factories by the prize that is considerably lower than the market value. As a matter of this, the value of operating costs can not be compensated and solid waste tariff can not be decreased down to the polygon rate. As for the European countries, the solid domestic waste generating power companies operate on legally fixed preferential terms (electric power supplied advanced prices) that are adopted for stimulation of biological waste power utilization.

In total, judging by the experience of utilization of Moscow solid domestic waste power it may be pointed out that the perspectives of bioenergetics development in terms of biological waste thermal treatment for the purpose of large Russian cities are of promising matter.