RU2637686C2 - Installation of environmentally safe high-temperature combustion of solid household and other organic wastes - Google Patents

Abstract

FIELD: heating.

SUBSTANCE: installation includes a receiving and unloading device, a waste boiler with a furnace, a combustion chamber, a gas cleaning unit. At the same time, a drying drum is installed between the receiving unit and the waste boiler furnace, drying out the solid household waste (SHW) to a residual moisture content of no more than 5% with flue gases from the boiler, burning of SHW in boiler furnace is performed using heated up to 700°C air, which is heated in heat-exchanging pipes laid in the walls of combustion chamber. Moreover, heated air is supplied in two places in the combustion chamber: under the SHW layer and above the SHW layer, while simultaneously burning both solid SHW particles and unburned gaseous pyrolysis products over the burning SHW layer, the molten slag is granulated in a water bath.

EFFECT: increase of efficiency of solid household wastes combustion.

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Description

The invention relates to the field of public utilities and is intended for the effective safe elimination of continuously increasing volumes of human waste - municipal solid waste (MSW).

Among the variety of methods for the elimination (disposal) of solid waste and other organic waste, thermal methods are recognized as the most effective, because reduce the volume of initial solid waste by tens of times, turning them into relatively safe ash and slag. At the same time, thermal methods for the disposal of solid waste are accompanied by negative processes with the formation of various types of toxic and carcinogenic products (CO, underburning of light hydrocarbons, NO _x , SO ₂ , Cl ₂ , dioxins, furans, heavy metals).

Effective suppression of these hazards can be achieved with high-temperature processing of solid waste (above 1200 ° C). At such temperatures, all types of organic, including harmful substances undergo irreversible destruction, turning into environmentally friendly compounds. If the formation of slag melt occurs during high-temperature processing of solid waste, its granulation in water leads to rapid curing, where heavy metals bind to harmless, complex compounds blocked by chemically resistant glass phase.

A known method of thermal disposal of solid waste by direct burning is widespread in world practice (Levin B. I. Use of municipal solid waste in energy supply systems. Energoizdat, M., 1982). This is a simple and relatively cheap way when solid waste, such as is, is burned in the furnace of an energy boiler without special processing. As a result of burning solid waste, the natural humidity of which varies widely, reaching 50 percent or more with an uncontrolled content of inorganic components (glass, concrete, ceramics, soil, etc.), the combustion temperature does not exceed 850 ° C, which eliminates the ability to effectively suppress synthesized by low-temperature combustion of harmful substances. To ensure environmental safety, these plants use complex and expensive gas purification systems, and in some countries they use special underflooding with natural gas or liquid fuel boiler in waste incineration boilers to raise the combustion temperature.

A known method and device for the incineration of municipal solid waste (Patent RU 2265773 C2, F23G 5/00, F23B 1/16), in which the temperature of the incineration of solid waste is brought to 1000 ° C, and filtering the flue gas is proposed through a layer of lime obtained by dissociation of limestone. The disadvantage of this method is the insufficiently high temperature of solid waste burning, which does not guarantee decomposition, in particular dioxins and furans, despite the fact that in the known invention, natural gas is used as an additional heating fuel.

A known method for the cyclic burning of municipal solid waste (Patent RU 2221197 C2, F23G 5/00), in which liquid oxygen is used to increase the combustion temperature of solid waste. The disadvantage of this method is the need to build an oxygen plant as part of the incinerator, this significantly increases the energy consumption, specific capital and production costs during the incineration of solid waste, moreover, the prerequisites for explosion hazard are created.

A known method of burning solid waste using plasma heating (Patent SU 1836603, F23G 5/00 Method for the thermal processing of municipal solid waste and a device for its implementation). The disadvantage of this method is the high consumption of electric energy with low efficiency of utilization, which will not allow you to create and operate production lines of significant power. The known method is useful and effective in laboratory conditions or, for example, for the disposal of small amounts of medical waste.

A known installation for the thermal processing of household waste (Patent RU 2303746 C2, F23G 5/14), adopted as a prototype, containing a receiving and unloading device, an incinerator boiler with a furnace, a combustion chamber, a gas treatment device, a waste heat boiler, a device for reheating flue gases for the combustion of gaseous fuels, as a result of which the temperature of the flue gases rises to 1300 ... 1400 ° C, ensuring guaranteed combustion of incompletely oxidized gaseous compounds, including the destruction of secondary dioxins ins and furans.

However, the known installation, adopted as a prototype, has the following disadvantages:

- for overheating of flue gases, additional fuel is used, which reduces the technical and economic efficiency of the process;

- heavy metals concentrated in ash and slag formed at relatively low temperatures (up to 1000 ° C) (the authors propose to overheat only the exhaust smoke products), contain heavy metals in an unbound form and retain a potential danger.

The aim of the invention is to provide a process for burning solid waste and other organic waste at temperatures not lower than 1300 ° C without attracting additional fuels, performing a thermochemical process entirely due to the energy contained in the solid waste, while the resulting ash and slag wastes in the molten state are granulated in cold water, turning into a solid vitrified product, reliably binding heavy metals in ash and slag.

The goal is achieved in that the installation of environmentally friendly high-temperature incineration of solid household waste and other organic waste, containing a receiving and unloading device, an incinerator boiler with a furnace, a combustion chamber, a gas cleaning device, is characterized in that a drying drum is installed between the receiving unit and the furnace of the boiler, drying of solid waste to a residual moisture content of not more than 5% by flue gases from the boiler, solid waste is burned in the boiler furnace using air heated to 700 ° C, which is heated etsya in the heat exchange tubes, installed in the walls of the combustion chamber, the preheated air is supplied in two places of the combustion chamber: a layer of solid waste and solid waste on the bed while ensuring combustion of both MSW solid particles and unburnt gaseous pyrolysis products over the burning MSW layer.

The invention is illustrated by the following schemes.

The figure 1 presents a diagram of the material and thermal balances of the traditional incineration of solid waste.

The figure 2 presents a diagram of the material and heat balance of incineration of solid waste, in which the solid waste and blast air are preheated.

The figure 3 presents a diagram of the material and thermal balances of an example of the practical application of the invention.

The figure 4 presents a longitudinal section of the installation.

The figure 5 presents a section of the furnace and the combustion chamber.

Position “1” on the diagrams of figures 1, 2, 3 indicates the firebox.

The installation contains a water bath for granulation of ash and slag melt.

Thermochemical basis of the guaranteed functioning of the invention are as follows.

Any solid waste collected in different regions at different times of the year always consists of three physical phases that are significantly different from each other:

combustible mass 38 ... 65% inorganic substance 12 ... 20% physical water 15 ... 50%

Such a significant dispersion of evidence determines the validity of the assertion that MSW is an extremely heterogeneous product.

However, a long-term analysis of MSW of Russian assembly in various cities of the country made it possible to find out the average statistical model of the phase composition of MSW, which looks like this:

combustible mass 49.7% inorganic substance 14.0% physical water 36.3%

The carrier of the energy potential of solid waste is a combustible mass represented by various organic products. The two other phases do not have an energy potential. The higher the proportion of the combustible mass in the MSW, the more heat will be generated during the combustion of the MSW.

According to numerous studies, the elemental composition of the combustible solid waste mass of the average Russian assembly is as follows:

carbon, C 52.2 ± 3.0% hydrogen, H ₂ 5.0 ± 1.6% oxygen, O ₂ 33.2 ± 2.6% nitrogen, N ₂ 1.5 ± 0.8% sulfur, S 0.5 ± 0.1% chlorine, Cl ₂ 0.2 ± 0.1% pyrogenetic ash 7.4 ± 1.5%

The theoretical calorific value of the combustible mass in MSW of the average Russian assembly, determined by the Mendeleev formula, is 4600 kcal / kg.

Knowing the calorific value of the combustible mass allows you to evaluate the calorific value of solid waste of any phase composition. So, the average model of the phase composition, in which the combustible mass is 49.7%, has an estimated calorific value:

Q _H = 0.497 × 4600 = 2290 kcal / kg

If part of the physical water is removed from the MSW, then the remaining, dry, part of the MSW will significantly increase the content of combustible mass and, therefore, increase the energy potential of the MSW. So, if the phase composition of MSW, presented above, is dried to a residual moisture content of 5%, then we obtain the MSW of the following phase composition:

combustible mass 86% inorganic substance 9% physical water 5.0%

Estimated calorific value of dry solid waste, where the amount of combustible mass is 86% (see above) will be:

Q _H = 3960 kcal / kg

The presented calculation clearly demonstrates the positive role of solid waste dehydration in increasing their energy potential.

Another additional effective factor in increasing the energy potential of solid waste, and therefore, increasing the temperature of combustion, is to increase the heat content (enthalpy) of dry solid waste heated during drying, and the heating of blast air necessary for combustion.

The heat content of dry solid waste is provided during drying of solid waste with flue gases leaving the boiler with a temperature of 300 ... 350 ° C. At this temperature, on the surface of the dried particles of solid waste, the temperature rose no higher than 250 ° C. An increase in the temperature of the dried solid waste above 250 ° C is unacceptable because of the threat of pyrolysis of the solid waste and filling the exhaust drying gases with pyrolysis gas.

The optimal drying device for drying solid waste is a rotating inclined chamber (drying drum), because only such a device of the drying apparatus will allow the MSW - a product structurally related, prone to clumping and freezing, guaranteed to move from the "cold" end of the drying device to the "hot" one, continuously turning over in the direction of the coolant flow.

Since the drying drum is directly connected with the furnace, the temperature of the dried solid waste does not have time to cool significantly. According to the results of experimental measurements, this temperature can be taken equal to 180 ° C, hence the heat content of solid waste acquired during drying can be calculated by the classical formula:

Where

m is the mass of dry solid waste, kg;

с - heat capacity of dry solid waste heated to 180 ° С (0.3 kcal / kg⋅rad);

t is the temperature of dry solid waste (180 ° C).

Substituting the known values in the formula (1), we obtain a simplified expression:

The heat content of the air supplied for the incineration of solid waste is provided by convective heating in a stack of pipes laid in the walls of the combustion chamber (see figure 2). The maximum possible temperature for heating steel pipes of the heat exchanger thermally insulated from direct heat exposure of the combustion products in the combustion chamber is 1000 ... 1050 ° C. Due to convective heat transfer, controlled by the speed of air through the pipes, the maximum heating of the air will be approximately 700 ° C. This value in the invention is considered optimal.

If the temperature of the heated air is 700 ° С, then its heat content will be determined by the formula (1), where t = 700 ° С, and с - 0.271 kcal / kg⋅rad:

Where

m is the mass of air supplied to the combustion, kg

To determine the combustion temperature of solid waste, we use the classical formula:

Where

t _D - actual temperature of fuel combustion, ° С;

Q is the calorific value of the fuel, kcal;

m is the mass of combustion products, kg;

с - heat capacity of the combustion products, kcal / kg⋅rad.

Let us compare the combustion temperatures of solid domestic waste of the average Russian assembly of “raw” and dried ones. Humidity of the first 36.3%, humidity of the second 5% (see above).

Suppose that 100 kg of raw MSW are burned with W = 36.3% and an ash content of 14%. The amount of heat released is equal to Q-2290-100 = 229000 kcal.

The amount of blast air with an excess coefficient α = 1.5 required for combustion, determined by standard methods, is 468 kg, the number of products of combustion, respectively, m = 568 kg, including slag 18 kg. The heat capacity of the gaseous products of combustion of 0.36 kcal / kg

Substituting the known values in the formula (4), we obtain the temperature of the gaseous products of combustion above 900 ° C.

A diagram of the material and thermal balances of the traditional MSW incineration process is presented in figure 1.

If you burn dried solid waste with a residual moisture content of 5% and an ash content of 9%, then the theoretical amount of heat generated:

Q = 3960 × 100 = 396000 kcal / kg

Due to the increase in the proportion of combustible mass in dry solid waste, the flow rate of blast air increases to 760 kg, the output of slag to 20 kg and the output of gaseous products of combustion to 840 kg. The heat content of dry solid waste, air and slag is determined by the formulas (1) ... (3). The temperature of gaseous and solid combustion products will exceed 1400 ° C.

The figure 2 presents the thermal and material balance of the process of burning solid waste, in which the solid waste and blast air are preheated.

The data presented indicate that in the case of using dehydrated and heated solid waste up to 180 ° C and heated blast air up to 700 ° C, the combustion temperature of the solid waste exceeds 1400 ° C, which guarantees the environmental safety of the combustion process.

Thus, the basis of the processes occurring in the installation, high-temperature combustion of solid waste and other organic products, which is the subject of the invention, are the objective laws of thermochemistry, guaranteeing the reality of the claimed invention.

The invention consists of the following components and parts (figure 4): a solid waste receiving unit (3), an unloading unit (10) with a water bath for granulation of molten slag (11), a drying drum (4), a high-temperature furnace (5), and a combustion chamber ( 7) with blowing fans and a package of air heating pipes, a boiler (9), a gas duct (8) for transferring the spent heat carrier (flue gases) to the dryer drum, flue gas cooling chambers (13) with a fan (12), a gas treatment unit (in the figure 4 is not shown).

Installation environmentally friendly high-temperature incineration of solid waste and other organic waste works as follows.

The solid waste arrives in the intermediate storage 1, from where the solid waste bucket of the clamshell crane 2 is transferred to the receiving device of the drying drum 4, where the solid waste is dehydrated for about one hour to a residual moisture content of about 5%. Drying of solid waste is carried out by the spent heat carrier (flue gases) from the boiler 9 by means of a connecting duct 8. The temperature of the cooled heat carrier is 300 ... 350 ° C. Since the temperature of the flue gases at the outlet of the boiler 9 reaches 500 ° C, the temperature of the waste heat carrier is reduced by mixing cold air with a fan 12 installed together with the mixing chamber 13 on the top of the boiler 9.

Dry solid waste with a temperature of about 180 ° C from the drying drum 4 directly fall into the high-temperature furnace 5, where it is burned at temperatures not lower than 1400 ° C. High-temperature combustion is achieved due to the heat content of dry solid waste and the heat content of blast air heated to 700 ° C in heat transfer pipes laid in the walls of the combustion chamber 6.

As a result of high-temperature combustion of solid waste, the mineral part contained in them is melted to a liquid fluid state. The slag melt is discharged into a water bath 11, where it is rapidly cooled, turning into a drop-shaped vitrified granules (granulated slag). Heated to a temperature of 1400 ... 1500 ° C, the coolant is sent to a steam or hot water boiler, where process steam or hot heating water is produced.

The spent coolant from the boiler 9 through the gas duct enters the drying drum 4, passing through the drying drum 4, the coolant saturated with the moisture evaporated from the MSW enters the gas purification unit, which consists of wet aerosol traps with the simultaneous hydrochemical neutralization of harmful gas compounds contained in flue gases.

An example of the practical use of the invention.

A city with a population of 500 thousand people has an annual output of solid waste of 200 thousand tons with an average humidity of 40% and an average ash content of 16%. With a plant operating mode of 360 working days per year, in three shifts, the working time fund will be 8640 hours per year and, therefore, the hourly capacity of a high-temperature solid waste incinerator will be:

P = 200000/8640 = 20.7 t / h

The phase composition of dry solid waste:

Combustible mass 44% 9.1 t Inorganic substance 16% 3.3 t Physical water 40% 8.3 t

At the preliminary stage, metal scrap and large inorganic fragments are removed from the MSW, which generally usually does not exceed 7% of the total mass of the MSW.

For drying:

MSW = 20.7- (20.7 × 0.07) = 19.2 t

As a result of drying in a drying drum, dry MSW of 11.5 tons is obtained having the following approximate phase composition and a temperature of about 180 ° C.

- combustible mass 9.1 t 79.1% - Inorganic substance 3.3 t 15.6% - Physical water 8.3 t 5.3% 11.5 t

The heat content of dry solid waste at the entrance to the high-temperature furnace, if the heat capacity of dry solid waste is 0.3 kcal / kg⋅rad.

i = 11500 × 180 × 0.3 = 621000 kcal

The elemental estimated composition of the combustible mass of solid waste:

carbon, C 52.2% hydrogen, H ₂ 5.0% oxygen, O ₂ 33.2% nitrogen, N ₂ 1.5% sulfur, S 0.5% chlorine, Cl ₂ 0.2% pyrogenetic ash 7.4%

The calorific value of the combustible mass Qн = 4600 kcal / kg.

If 11.5 tons of dry solid waste contains 9.1 tons of combustible mass, therefore, the theoretical amount of heat during the combustion of dry solid waste will be released:

Qn = 9100 × 4600 = 41.86 Gcal

We calculate the need for blast air necessary for burning 11.5 tons of dry solid waste.

The carbon content of 11.5 tons of dry solid waste:

C = 11.5 × 0.522 = 6.003 t

same hydrogen content:

N = 11.5 × 0.05 = 0.575 t

same oxygen content:

O = 11.5 × 0.332 = 3.181 t

same sulfur content:

S = 11.5 × 0.605 = 0.0575 t

Oxygen demand for carbon oxidation:

C + O ₂ = CO ₂

6003 kg C + 16008 kg O ₂ = 22011 kg CO ₂

the same for burning hydrogen:

2H + 0.5O ₂ = H ₂ O

575 kg H + 4600 kg O ₂ = 5175 kg H ₂ O

the same for burning sulfur:

S ₂ + 2O ₂ = 2SO ₂

57.5 kg S + 57.5 kg O ₂ = 115 kg SO ₂

Theoretical amount of oxygen required for burning solid waste:

O ₂ = 16008 + 4600 + 57.5 = 20665.5 kg / h

Subtract the own oxygen of solid waste, equal to 3818 kg, and find the theoretically necessary amount of air:

B = (20665.5-3818) / 0.233 = 72307 kg / h

The actual amount of air is determined taking into account the excess of oxidizing agent, in case of layer-by-layer combustion this coefficient is taken α = 1.4 ... 1.6. We take α = 1.5, then the air consumption for burning 11.5 tons of dry solid waste will be equal to:

B = 72307 × 1.5 = 108460 kg / h (84000 nm ³ / h)

If the blast air is heated to 700 ° C, then it will acquire a heat content equal to (at C = 0.271 kcal / kg deg):

i = 108460 × 700 × 0.271 = 20.57 Gcal

If 11.5 tons of dry solid waste are heated to 180 ° C, then their heat content will be:

i = 11500 × 180 × 0.3 = 0.621 Gcal

We determine the combustion temperature by the formula:

t _k = Q / mc, ° С

Where

Q = 41.86 + 20.57 + 0.621 = 63.051 Gcal (taking into account the combustion efficiency of 0.94, Q = 59.3 Gcal);

m is the mass of combustion products, 11500 kg + 108460 kg = 119960 kg;

s - average heat capacity of the combustion products, 0.35 kcal / kg⋅ grad;

t _to = 59300000 / (119960 × 0.35) = 1410 ° С

The performed calculations are presented in the form of a diagram of material and thermal balances, which are presented in figure 3.

Claims (1)

Installation of environmentally friendly high-temperature incineration of solid household waste (MSW) and other organic waste, containing a receiving and unloading device, an incinerator boiler with a furnace, a combustion chamber, a gas cleaning device, characterized in that a drying drum is installed between the receiving unit and the furnace of the boiler, which carries out drying of the MSW to a residual moisture content of not more than 5% by flue gases from the boiler, solid waste is burned in the boiler furnace using air heated to 700 ° C, which is heated in a heat exchange pipes laid in the walls of the combustion chamber, and heated air is supplied in two places of the combustion chamber: under the MSW layer and above the MSW layer, while simultaneously burning both solid MSW particles and unburnt gaseous pyrolysis products above the burning MSW layer, the molten slag is granulated into water bath.

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