RU2128806C1 - Method of burning oil coke - Google Patents

Abstract

FIELD: power engineering. SUBSTANCE: coke is burned jointly with coal at grinding degree corresponding to that of lean coals and with optimal oil coke proportion corresponding to yield of volatile fuel constituents determined by the following formula: b_coke/b_coal = f(V_coke-vol/V_coal-vol) where b_coke and b_cole, respectively, are portions of oil coke and coal, weight consumptions in unit time; V_coke-vol and V_coal-vol, respectively, are yields of volatile components of oil coke and coal, %. Pulverization of oil coke and coal is performed jointly or separately followed by mixing coke and coal dusts before entering burner, or they are introduced into burner separately. EFFECT: enabled utilization of coke as power-plant fuel.

Description

 The invention relates to the field of power engineering, in particular to a technology for burning petroleum coke.

 Petroleum coke is a product of deep oil refining, which in our country has recently been used as fuel.

 According to the conditions of storage, preparation and organization of oil combustion, it approaches coal, has a low volatile yield (like lean coal, anthracite, which makes it difficult to ignite and burn out coke particles).

 Petroleum coke has a high specific heat of combustion (7800 - 8100 kcal / kg), which reduces the mass of material transported and processed at TPPs and increases the temperature of the flame in the furnace.

 A known method of burning petroleum coke, in which to maintain stable combustion, additionally burn natural gas ("World Thermal Power", N 2, 1994, S. 43 - 44).

 The disadvantage of this technical solution is the need to include other types of fuels (highly reactive) in the fuel balance of the coal station, which requires the laying of additional lines, systems for supplying and storing these fuels.

 A known method of burning petroleum coke in boilers with a circulating fluidized bed (CCS). These boilers provide a high degree of carbon combustion, do not require the burning of an additional higher-quality fuel (World Electric Power Industry, N 2, 1994, p. 44).

 In our country, there are no similar designs of furnace devices.

 The technical challenge facing the proposed technical solution is to ensure the possibility of using petroleum coke as energy fuel by burning the latter in the chamber furnace devices of existing boiler units operating on various types of coal.

где b_к - доля нефтяного кокса в коксоугольной смеси (массовый расход в единицу времени);
b_у - доля каменноугольного топлива в коксоугольной смеси, (массовый расход в единицу времени);
V $\genfrac{}{}{0ex}{}{\text{г}}{\text{лк}}$ - выход летучих нефтяного кокса на горячую массу, %;
V $\genfrac{}{}{0ex}{}{\text{г}}{\text{лу}}$ - выход летучих каменного угля на горячую массу, %.To solve the problem by the known method of burning petroleum coke, based on mixing the latter with other types of energy fuel, petroleum coke is burned in boilers with chamber furnace devices together with coal fuel; the fineness of grinding of coke corresponds to the fineness of grinding of lean coals, and the optimal proportion of petroleum coke in the mixture corresponds to the yield of volatile constituent fuels and is determined by the ratio

where b _to - the proportion of petroleum coke in the coke coal mixture (mass flow rate per unit time);
b _y - the proportion of coal fuel in the coke coal mixture, (mass flow rate per unit time);
V $\genfrac{}{}{0ex}{}{\text{g}}{\text{lx}}$ - yield of volatile petroleum coke to the hot mass,%;
V $\genfrac{}{}{0ex}{}{\text{g}}{\text{lu}}$ - yield of volatile coal on the hot mass,%.

 Dust preparation of petroleum coke and coal in this case is carried out jointly or separately, followed by mixing before entering the burner or provide their separate supply.

 The proposed technical solution is illustrated by drawings.

 In FIG. 1 is a flow chart of the preparation of a (joint) coke-coal mixture for combustion; in FIG. 2 presents the technological scheme of separate dust preparation.

 The proposed scheme (Fig. 1) contains a petroleum coke warehouse 1, a coal warehouse 2, a metering and mixing unit for fuel components 3, a fuel supply to the fuel bunkers 4, a drying and dust preparation system 5, a dust bunker 6 and then into the burner 7 or bypassing the bunker dust 6, through a dust pipe direct injection 8 into the burner 7.

 FIG. 2. The scheme for separate supply and dust preparation of fuel contains 2 parallel threads, each of which includes a fuel storage 1, 1, fuel supply 2, 2, a drying and dust preparation system 3, 3, which are combined at the inlet to the dust bin 4, and further connected by a dust pipe, with a burner 5 (for a dust system with an industrial hopper), or directly into a burner 5 through a mixing unit 6 (for a vacuum system with direct injection).

The use of the present invention provides for the burning of petroleum coke in pulverized-coal chamber furnaces of power boilers mixed with project solid fuel, which will make it possible to level out some specific properties of petroleum coke (by ignition, ignition, effect on corrosion processes, high carbon content in the convection shaft, increased emission of sulfur oxides), while the maximum proportion of petroleum coke in the coke coal mixture is determined by the design of the furnace burner Twa and project fuel quality. The burning of petroleum coke when it is mixed with all types of coal used in the energy sector (up to 10-15% of the total mass fuel consumption) is fundamentally possible with varying efficiencies in almost all existing designs of furnace-burner devices. However, in this case, and in other modes of using coke, an indispensable condition is to ensure a certain fineness of coal grinding - up to R ₉₀ ≤ 8%.

An increased proportion of coke in the mixture with the project fuel can be provided in a certain class of existing furnace burner devices, which can be ranked by the degree of suitability for coke burning as follows:
1) High-temperature fire chambers with limited heat removal to the shielding heating surfaces in the zone of formation of the torch — the furnace with pinch in the lower part with completely closed lining mass screen tubes (ensuring the temperature in the core of the torch to 1650 - 1750 ^o C, are optimal for igniting and burning petroleum coke) allows you to burn low-reaction fuels - lean coals, anthracites with slag removal in the molten state), as well as furnaces with an incendiary belt in the area of the burner belt up to a height of 3 m, used To effectively burning lean coals.

2) Fire chambers with a compact, closed torch, which is organized by a large number of counter-mounted vortex burners (from the front and back of the fire chamber), are also suitable for burning petroleum coke (both autonomously and as a mixture in coal); such boilers are designed for coal brand "SS", close to lean;
3) With this arrangement, with an increase in the burner pitch and individualization of the flames, the conditions for burning petroleum coke (as well as any lean coal) worsen. Such solutions are used in many types of boilers designed for Ekibastuz coal, which is only conditionally defined as lean. Here, probably, we can only talk about co-combustion with project fuel.

 4) The counter arrangement of the burners on the side walls of the screened furnace is less favorable for the use of petroleum coke. The frontal arrangement of the vortex burners is due to the increase in this case the intensity of heat removal from the flame.

 5) Adverse conditions for the combustion of petroleum coke in furnaces with once-through burners, including with their tangential arrangement, as well as with flat torches.

 The problems of organizing the use of petroleum coke in the energy sector are not limited to sustainable ignition and complete burnout. The most important thing in this case is the reliability of equipment.

 1) The nature of the corrosion processes has not been studied for co-burning petroleum coke with coal, however, it can be assumed that significantly different from the mechanism of corrosion processes in fuel oil boilers, it is similar to the conditions for burning sulfur coals, for which effective methods have been developed to prevent high-temperature and low-temperature sulfur dioxide. There is no experience in the use of solid fuels with a high content of vanadium (characteristic of petroleum coke) in the energy sector; special studies will be needed on the possibility of developing vanadium corrosion of high-temperature heating surfaces.

 2) Preliminary calculations show that burning coke and a coke-coal mixture shifts the core of the torch to the upper part of the furnace, increasing somewhat the temperature at the inlet to the superheater, as well as in the area of the air heater, possibly above the permissible level. Maintaining calculated (or close to them) indicators for the temperature of the metal of the heating surfaces is carried out by choosing an acceptable fraction of coke in the mixture with coal, by regulating the total excess of air in the furnace.

3) To prevent deposits in convective heating surfaces, ash collectors of carbon particles prone to fire, it is advisable not to exceed the proportion of coke in the mixture with coal above 60 - 70 ^o C; Before the planned shutdown of the boiler, in order to remove a possible accumulation of carbon-containing particles, switch to burning settlement coal. In case of unscheduled shutdowns, clean and wash.

 Co-combustion of coke and project solid fuels reduces the environmental stresses that may arise from autonomous coke burning.

 The environmental properties of petroleum coke are determined by the minimum content of mineral inclusions and, accordingly, the insignificant emission of ash and slag particles during coke burning; high content in coke (in its mineral part) of heavy metals — vanadium, nickel; high content of sulfur compounds in the organic part of coke.

In general, environmental problems in the combustion of a coke coal mixture are not a limiting factor in the inclusion of petroleum coke in the fuel balance of thermal power plants. They are solved:
- the choice of an object for which there is a certain environmental reserve for the additional release of sulfur dioxide;
- use of coke at thermal power plants, for which project fuel is close in its environmental characteristics to petroleum coke;
- implementation, if necessary, of additional technological solutions;
- the choice of acceptable in a particular case, the composition of the coke-coal mixture.

The formation of a coke-coal mixture of a given composition can be carried out:
- directly in a coal warehouse by layer-by-layer stacking of coke and coal in stacks;
- when separately storing coal and coke in a warehouse in separate stacks and creating a special mixing complex;
- when coal and coke are separately delivered to the fuel supply unit of the TPP by feeding coal and coke to separate receiving hoppers with an adjustable gate for delivery to two parallel conveyors unloading the transported material onto a common conveyor belt.

Thus, the use of petroleum coke in the energy sector in the form of a coke coal mixture allows:
1) use the existing equipment of thermal power plants;
2) reduce the time for the inclusion of petroleum coke in the fuel balance of the energy sector;
3) to provide an effective solution to issues of equipment reliability during coke burning;
4) to weaken the manifestation of certain environmentally unfavorable properties of petroleum coke.

1. Combined burning of petroleum coke and coal fundamentally changes the nature of deposits on high-temperature heating surfaces and the conditions of high-temperature vanadium metal corrosion:
- if, when burning ashless vanadium-containing fuel (fuel oil, peat coke), sticky, hard to remove deposits form on the heating surfaces in the furnace. To reduce the intensity of corrosion processes in fuel oil boilers, an additive is introduced containing a certain combination of magnesium, aluminum, silicon, and the resulting dry deposits prevent oxygen diffusion to the metal surface and thereby reduce the intensity of corrosion;
- when burning a coke-coal mixture, the role of an additive can be played by ash particles of coal containing a sufficient amount of these substances that increase the melting temperature of the ash mixture: practice shows that burning solid fuel with vanadium fuel oil highlighting in no case led to the development of high-temperature vanadium corrosion. The data of tests carried out by the applicant on a boiler using a coke coal mixture show that the deposits formed in this mode on the heating surfaces (screens, superheater) are dry, easily removable, and unstable, which indirectly indicates that there is no condition for the development of vanadium corrosion.

 2. Combined burning of petroleum coke and coal changes the nature of deposits in the convective duct. Instead of the carbon content in the deposited from 50 to 80% typical for the coke burning mode (which creates a real danger of ignition of these deposits and destruction of the air heater), when burning a coke-coal mixture, the carbon content in ash deposits in the convection shaft does not exceed 15 - 18%, which practically eliminates the possibility of fire and ensures the reliability and safety of convective heating surfaces in thermal mode.

 3. When co-burning petroleum coke and coal due to the presence of abrasive ash particles in the flue gas stream, it ensures the removal of coke ash particles outside the boiler path and their collection in ash collectors. With the autonomous burning of coke (like fuel oil), the problem arises of removing deposits with a high vanadium content having significant toxicity from heating surfaces, which requires special measures to ensure the necessary sanitary and hygienic requirements for the safe work of personnel.

 4. The influence of the increased sulfur content in petroleum coke and the increased emission of sulfur dioxide are somewhat offset by the combustion of the carbon-coal mixture by the presence in the flue gases of a significant amount of coal ash particles (calcium compound content), the ability to bind from 10 to 50% of the total amount of sulfur dioxide working path of the boiler.

 5. When autonomous combustion of petroleum coke in chamber furnaces, which is a low-reactive fuel, the ignition conditions of coke particles are entirely determined by radiation from the enclosing surfaces coated with energy-resistant lining, which are not always found in combustion devices.

 When coke is burned in a mixture of natural solid fuels in furnace-burner-rated coal, reliable stabilization of the pulverized coal flame and the necessary conditions for sufficiently early ignition of coal dust are ensured. Due to the intense heating of coke particles located directly in the high-temperature pulverized coal flame to the ignition temperature, the development of the coke dust flame is initiated (regardless of the effect of radiation in the enclosing surfaces). At various densities and volumes of the pulverized-coal plume, various conditions for ignition of coke particles are formed.

 Co-combustion of coke with project solid fuel eliminates the need for reconstruction of existing dust preparation systems (due to the reduction in the mass of the processed material during the transition from coal to coke).

 6. Autonomous burning of petroleum coke requires the organization of special systems for cleaning flue gases from ash particles of coke with a high carbon content, electrophysical properties, the possibility of sticking on electrodes, and hydrophobicity.

 Combustion of a coke coal mixture allows the efficient use of existing ash collection systems.

Claims (2)

1. A method of burning petroleum coke, based on mixing it with other types of energy fuels, characterized in that it is burned in boilers with chamber furnace devices together with coal fuel, while the fineness of grinding of coke corresponds to the fineness of grinding lean coal, and the optimal proportion of petroleum coke corresponds to the release of volatile constituent fuels and is determined by the ratio

where b _k is the proportion of petroleum coke in the coke coal mixture; mass flow in units time;
b _y is the proportion of coal fuel; mass flow per unit time;
V $\genfrac{}{}{0ex}{}{\text{g}}{\text{lx}}$ - the yield of volatile petroleum coke in the combustible mass,%;
V $\genfrac{}{}{0ex}{}{\text{g}}{\text{lu}}$ - the yield of volatile coal in the combustible mass,%.  2. The method according to p. 1, characterized in that the pulverization of petroleum coke and coal is carried out jointly or separately with subsequent mixing before entering the burner or carry out their separate supply.

Images