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Abstract

Contents

Introduction

One of the urgent tasks of thermal energy in Ukraine is the replacement of natural gas by local energy resources - coal, carbonaceous waste, biomass and other solid fuels. On TEP to date, this problem is basically solved: in 2007, compared with the previous decade, natural gas consumption decreased by almost 10 times, and on coal-fired power units is not more than 1 billion m3 per year. Next in importance is the gas consumer utility and industrial power system.

At the same time on the fore the problem of finding additional resources, cheap energy, the use of which can be arranged in a relatively short period of time and does not require substantial investment. The use of such relatively cheap energy even in low power will allow to some extent to stabilize the fuel and energy balance of the country.

One solution to the problem of finding additional fuel resources is the utilization of waste or recyclable is not free at the moment of flammable products of different industries. In this regard, it may be very promising use of waste products and the production of coke as energy sources for the production of thermal or electric energy. Thus, waste coke production (coke oven gas and coal slurries with high ash content) principle can serve as an additional source of fuel resources to produce heat and electricity.

In order to obtain more cheap energy for reliable operation of TEP YCCP in increased consumption of thermal energy, work was undertaken, in which as an object of research has been accepted of high-carbon sludge coking coal. The most promising area has been recognized on the basis of preparation of coal-water slurry coal fuel and burning it together with the coke oven gas.

1. Situation and objectives of research

1.1 The use of coal for combined incineration of sludge in the form of coal-water fuel, together with the staff in the world

The absence in Ukraine developed its own gas production and the oil industry makes it necessary to import hydrocarbon energy, which puts the country in a heavy economic dependence on foreign suppliers. In these circumstances, the main source of energy becomes coal production volumes which, despite some increase in recent years is clearly lagging behind the needs of the power system. The increase in the volume of coal can only be done by radical reconstruction and construction of new mines, which takes time and involves considerable investment.

Under these conditions, there is the problem of finding more cheap energy and improving technologies of solid fuel. This circumstance is the primary motivating factor for use in the heat of high-coal tailings (sludges). In this context, it seems more appropriate to use extracted from the tailings pond sludge of high-carbon as a starting material for the preparation of coal-water fuel. An attractive factor in this case is the fact that coal is already finely ground and therefore, power consumption of the process of preparation WCF will be significantly reduced as compared with ordinary coal.

The effectiveness of co-firing (in English literature - the technology «co-firing») of coal-water fuel, prepared on the basis of coal slurry to increase significantly when they are co-firing with other waste products, such as for example coke oven gas.

Great experience on the use of technology «Co-firing» is the United States. The United States do not apply to countries lacking oil and therefore the interest in the production and use of WCF in this country is due mostly to discard large amounts of coal dust, which when accepted technology waste coal production.

Corporation for Research in Energy and the Environment (EER), Ohio, a research center of the University of Pennsylvania, by Penelec and some others made a large amount of theoretical and experimental studies on the preparation of WCF low concentrations (up to 50% ash content 10 - 15 %) without the use of chemical additives of fine coal supplied by the production line concentrator or impounded in the dumps.

To enrich the fine coal were used chemical extraction, selective oil agglomeration of coal, gravity and flotation methods. Burning WCF with pulverized coal at a ratio of 1:4 is produced in the boiler of 32 MW capacity at the processing plant in Homer City, as well as power plants in Seward boiler capacity of 130 tons of steam per hour.

Researchers believe that the preparation of the WCF small high-ash coal can create a market for the most part the material is considered waste production and at the same time reduce the cost of fuel to consumers.

1.2 Estimated object of implementation and tasks of research. The alleged object implementation is TEP YCCP

TEP YCCP operate boilers TP 35-39 with parameters:

Steam output – 35 t/h;

Superheated steam temperature of – 440 °С;

Feed water temperature – 125 °С;

The heat capacity of superheated steam – 790,6 kcal/kg;

The heat capacity of the feedwater – 131,1 kcal/kg;

Efficiency (For reference data) – 90%;

Fuel - coke gas calorific value (according to YCCP) – 4200 kcal/m3;

Fuel consumption (without purging):

В = 6107 m3/h;

All the supply of thermal energy E = 25,65 Gcal/h.


Research tasks

Explore the qualitative characteristics of coal slurry dispersion medium of the conditions of their use as starting materials for the preparation of water-coal fuel.

To conduct laboratory studies of coal-water fuel technology of preparation of high-sludge-based coking coal, taken from the slurry tank YCCP, to determine the structural and rheological parameters and sedimentation WCF.

Develop recommendations and technical solutions for preparation and combustion of coal-water fuel based on coal slurry.

2. Features burning sludge to the Constitutional Court and the requirements for fuel preparation

Technology for combusting solid fuels in the boiling layer are in modern, environmentally friendly, with low requirements to the quality of the fuel and to adjust a load in a wide range. BL-boilers are well utilized for a range of 1,9-70 MW thermal power (steam capacity 2-75 t/h). Their main advantages over a fixed-bed boilers with flaring in terms of requirements for fuel are:

Thus, for slurries of high-combustion in the BL is most preferred. On the other hand, since the majority of the boilers with the BL used crushed coal, experience in development and operation of boilers for sludge is limited. This section discussed the difficulties associated with the organization of the burning sludge in the BL, and possible ways to overcome them.

shema_CKS

Figure 1 - Stand modified CBL - 0,02 to study the combustion of solid fuels in the BL and the CBL: 1 - coal bunker, 2 - screw feeder, 3 - firebox with boiling layer, 4 - perforated grille, 5,6 - burners for ignition, 7 - cyclone, 8 - tract circulating ash, 9 - a device for plum the bottom ash, 10 - a device for plum the circulating ash, 11 - condenser, 12 - inert material hopper, 13 - storage of fly ash, 14 - smoke exhaust damper.

The furnaces with the BL used fuel class size from 0-3 mm to 0-13 mm. The layer of lift gas air stream supplied from below through the grate, balances the weight of the particles, which is why there is a fluidized - an intensive heat and mass transfer and adjustment section of the bed. In the space above the layer of open area, and consequently also the gas velocity, smaller (up to 1.5-2.5 m/s), and most of the particle layer made from falling back into the bed. Due to the fact that burning particles, the proportion of which layer is small, surrounded by inert burning particles do not overheat, and the average temperature of the bed does not exceed 950°С. Under these conditions, the generation of nitrogen oxides is low, and there is a possibility of binding sulfur limestone fed to the bed to chemically inert gypsum, so that the boilers with the BL meet modern environmental standards without the use of sulfur and nitrogen removal. Low specific rate of carbon combustion and its concentration in the layer are offset relative to the large mass and the height of the layer (1,0-1,2 m) and deep burning most of the particles is achieved by their long residence time in the bed. In boilers with the BL heating surface is placed on the roof of the furnace, in the convective mine, as well as using surface immersed directly in the layer.

Although, in contrast to the fixed bed, the presence of fuel fines is not critical for the process of combustion in the BL, it significantly reduces its efficiency. The fact that the imposition of a layer of fines smaller than 0,5 mm is not returned to the bed, and because the temperature in the space above the bed at 200-300°С lower than in the bed, the fines and combustion ceases. Attempts to catch the breeze and return it to the post-combustion into the layer of ineffective because trapping efficiency cyclones for particulate matter less than 70%. The desired condition is a fuel preparation fines agglomeration; due to the high residence time and limited combustion temperatures (below the melting point of ashes) pellets with up to 13 mm in a fluidized bed completely burn out. However, as to completely remove the fines from the real fuel is not possible, the loss of carbon entrainment to date is one of the most significant shortcomings of combustion technology in the BL. Another disadvantage is the difficulty of ensuring uniform supply of fuel and mixing of the material layer in boilers high power and hence a large area array.

Also, the benefits of the BL are possible:

Selecting a fluidized bed technology is dependent on the thermal power plant and the used fuel. For steam below 50 t / h of crushed coal and a relatively low content of dust-like fines quite suitable boiler classical BL, including converted from an old boiler with a fixed bed. Several dozen furnace fixed bed at the coal enterprises of Donbass layer was renovated in the boiling layer, to date, they have developed a resource and taken out of service. For intermediate steam production and use of sludge coking coal can recommend the boiling layer technology with the return.

This master's work is not completed yet. Final completion: December 2015. The full text of the work and materials on the topic can be obtained from the author or his head after this date.

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