RU2521508C1 - Method of thermal deactivation of biogas of solid domestic waste landfills - Google Patents

Abstract

FIELD: ecology.

SUBSTANCE: for environmentally safe thermal deactivation of biogas of solid domestic waste landfills the biogas is removed by drainage and creation of forced vacuum gauge pressure. Then the moisture content in the removed biogas is reduced due to the sharp decrease in temperature, the biogas is compressed and the preliminary purification of biogas from moisture and hydrogen sulphide is carried out, it is filtered from dust, and the biogas is burnt. The exhaust flue gases are cooled and purified from acidic components and halogenated hydrocarbons. At that in the flow of flue gases and the concentration of hydrogen sulphide and acidic gaseous compounds of sulphur and carbon are measured continuously, taking into account which the dynamic consumption adjustment of sorbents and the reagent is carried out based on the previously obtained experimental data of approximating regression relationships.

EFFECT: increase in environmental safety, it stabilises the operation of the gas purification system and reduces the consumption of reagents.

3 cl, 5 tbl

Description

The invention relates to a technology for thermal neutralization of biogas and is intended to reduce their negative impact on the environment and increase the efficiency of cleaning emissions from biogas neutralization plants.

Known methods for collecting biogas generated from organic waste at landfills (GB 2466554 A, published. 06/30/2010), according to which in the process of burning biogas flue gases are formed, which are removed from the combustion zone and then fed to the apparatus for the production of thermal and electric energy. Thus, during biogas combustion, flue gases after treatment plants are emitted into the atmosphere.

The traditional biogas utilization scheme according to this invention also has a traditional drawback: after biogas is burned, flue gases have significant fluctuations in the concentration of pollutants, which makes it difficult for the biogas to be environmentally friendly to neutralize and the stability of reaching standard concentrations of pollutants at the outlet of the flue gas cleaning system.

The prototype of the proposed invention is a method of environmentally friendly disposal of landfill biogas (RU 2362636 C2, published. 07/27/2009) using a biothermal photoelectrocatalytic cogeneration unit, in which flue gases are released into the atmosphere during biogas burning.

The disadvantage of the invention is the lack of preliminary cleaning of the landfill biogas from fine dust, which does not allow to achieve standard concentrations of pollutants in the landfill biogas with significant fluctuations in its chemical composition.

In the invention, a technical result is achieved, consisting in the stability of the gas cleaning system and reducing the cost of gas cleaning by reducing the consumption of reagents for the purification of exhaust gases.

The specified technical result in the proposed invention is achieved as follows.

A method of environmentally friendly thermal neutralization of biogas from solid waste landfills involves the extraction of biogas through drainage and forced vacuum, reducing the moisture content in the extracted biogas due to a sharp decrease in temperature, compressing biogas, preliminary cleaning of biogas from moisture, hydrogen sulfide and dust.

Then the biogas is burned, as well as the cooling and purification of the flue gases from acid components and halogenated hydrocarbons.

In the flue gas stream, the concentrations of hydrogen sulfide and acidic gaseous sulfur and carbon compounds are continuously measured.

Taking into account the measured concentration values, dynamic adjustment of the sorbent and reagent consumption is carried out on the basis of approximating regression ratios obtained previously from experimental data.

At the same time, biogas is cleaned of dust by filtration.

Also approximating regression relations are as follows:

$$t=c_0+c_{\mathrm{one}}\cdot \exp \left(c_2\cdot L\right)\cdot \sin \left(c_5\cdot L+c_3\right)\cdot {\left(c_5\cdot L+c_{\mathrm{four}}\right)}^{-\mathrm{one}}\left(\mathrm{one}\right)$$

$$\Delta P=a_0+a_{\mathrm{one}}\cdot L+a_2{L}_2+a_3\cdot L_3\left(2\right)$$

, где $$C_i=b_{\mathrm{one}}\cdot L+b_2\cdot L^2+b_3\cdot L^3+b_{\mathrm{four}}\cdot L^{\mathrm{four}}\left(3\right)$$

where

t is the temperature of the flue gases at any point in the gas cleaning tract;

c ₀ , c ₁ , c ₂ , c ₃ , c ₄ - constants of equation (1);

a ₀ , a ₁ , a ₂ , a ₃ - constants of equation (2);

b ₁ , b ₃ , b ₃ , b ₄ - constants of equation (3);

Ci is the concentration of the i-th pollutant in the flue gases at any point in the gas treatment path;

ΔР - rarefaction of flue gases at any point in the gas cleaning tract;

L is the distance from the origin to the point of definition of the parameter.

Cleaning the landfill biogas to the normative concentrations of hazardous components is possible only by combining the cleaning of flue gases from biogas combustion products at the outlet of the biogas neutralization unit with its preliminary purification from fine dust sorbing toxic components in the landfill and desorbing them during biogas combustion.

The invention is as follows.

First, the collection of landfill biogas is carried out by means of vertical gas drainage and forced extraction of biogas from the landfill by creating a vacuum of about 100 kPa.

Then, the moisture content in the recoverable landfill biogas is reduced with a sharp drop in temperature from 40 ° C to 60 ° C, which is typical for the deep layers of solid waste landfills due to biochemical fermentation reactions, to ambient temperature.

After that, filtration purification of biogas from fine dust is carried out, thus releasing biogas from toxic components sorbed in the body of the landfill.

Then biogas is compressed to a working pressure of 0.2-0.5 MPa.

After compression, biogas is cleaned. The process is divided into two stages: first, the selective removal of acidic components from biogas is carried out by adsorption on a sorbent, and then the halogenated hydrocarbons are separated by adsorption on special activated carbon.

After cleaning, additional moisture is removed from biogas by adsorption on a sorbent, which eliminates corrosion processes, as well as provides protection against drip shocks and prevents capillary condensation at the adsorption stage of halogenated hydrocarbon removal.

Then carry out the thermal neutralization of biogas by burning. To ensure explosion-safe regimes of biogas combustion with a decrease in methane concentration of less than 10% of the lower explosive concentration limit, natural gas is additionally supplied for combustion in an amount that ensures safe combustion of the mixture. The combustion air of the mixture is supplied with an excess coefficient of 1.05-1.1 at ambient temperature and with a pressure of up to 0.36 MPa.

In the resulting stream of flue gases exhausting after burning biogas, their temperature and pressure are determined.

Flue gases are cooled during heat exchange with chemically purified water to a temperature of about 160 ° C. The nominal consumption of chemically purified water at a temperature of 20 ° C will be 15.1 m ³ / h. The minimum consumption of chemically purified water at a temperature of 20 ° C will be 8.6 m ³ / h. The temperature of chemically treated water supplied during the heat exchange process must be at least 60 ° C, and leaving 115 ° C.

In the flue gas stream, a continuous measurement of the concentration of polluting carcinogenic compounds in the form of acidic components and halogenated hydrocarbons is carried out.

The flue gas stream is cleaned of these contaminants by chemical adsorption with calcium hydroxide and activated carbon.

When cleaning flue gases, the flow rate of sorbents and reagent is dynamically adjusted taking into account the concentrations of acid components and halogenated hydrocarbons measured in the flue gas stream.

Dynamic adjustment of the flow rate of the sorbent and reagent is carried out by calculating the difference between the measured flow rate of the sorbent and the estimated flow rate of the sorbent. The calculated value of the sorbent and reagent is calculated using approximating regression ratios obtained on the basis of preliminary experimental data.

Approximating regression relationships are as follows:

, где

where

G _ic - sorbent consumption (kg / h);

a _1c , b _1c , c _1c - constants of equation (4);

t is the temperature of the flue gases in the gas cleaning tract, ° C; (150 ÷ 300 ° C);

P is the flue gas pressure in the gas cleaning tract, MPa; (0.09 ÷ 0.11 MPa);

C _i is the concentration of the i-th pollutant in the flue gases in the gas treatment path, mg / m ³ (10 ÷ 100 mg / m ³ ).

, где

where

G _ip - reagent consumption (l / min);

a _1p , b _1p , c _1p are constants of equation (5);

t is the temperature of the flue gases in the gas cleaning tract, ° C; (150 ÷ 300 ° C);

P is the flue gas pressure in the gas cleaning tract, MPa; (0.09 ÷ 0.11 MPa);

C _i is the concentration of the i-th pollutant in the flue gases in the gas treatment path, mg / m ³ (10 ÷ 200 mg / m ³ ).

In this case, a _1c , b _1c , c _{1c are the} constants of equation (4) and a _1p , b _1p , and _{1p the} constants of equation (5) are obtained as a result of mathematical processing of the experimental data and are presented in table 1 and table 2.

Table 1  equation constants (4) a _1c b _1c c _1c Value 9.8 0.4 0.018 table 2  equation constants (5) a _1p b _1p c _1p Value 2.98 0.87 0,045

Correction is carried out on the basis of previously obtained experimental data, approximating the regression relations describing the change in the physicochemical parameters of the flue gas stream along the gas purification path.

These approximating regression relationships are as follows:

, где

where

t is the temperature of the flue gases at any point in the gas cleaning tract;

c ₀ , c ₁ , c ₂ , c ₃ , c ₄ - constants of equation (1);

a ₀ , a ₁ , a ₂ , and ₃ are the constants of equation (2);

b ₁ , b ₂ , b ₃ , b ₄ - constants of equation (3);

C _i is the concentration of the i-th pollutant in the flue gases at any point in the gas treatment path;

ΔР - rarefaction of flue gases at any point in the gas cleaning tract;

L is the distance from the origin to the point of definition of the parameter.

Moreover, the constants of equation (1) are obtained as a result of mathematical processing of experimental data and are presented in table 3.

Table 3  constants of equation (1) from ₀ c ₁ from ₂ from ₃ from ₄ Value 134 1.76 * 10 ³ -2.46 9.73 * 10 ^-4 0,048

The constants of equation (2) are obtained as a result of mathematical processing of experimental data and are presented in table 4.

Table 4  constants of equation (2) a ₀ a ₁ a ₂ a ₃ Value -1.65 1,66 -0.039 4.03 * 10 ^-4

The constants of equation (3) are obtained as a result of mathematical processing of experimental data and are presented in table 5.

Table 5  constants of equation (3) SO ₂ Hcl NOx Hf b ₁ 9.42 6.12 15,5 0.725 b ₂ -0.215 -0.138 -0.441 -0.021 b ₃ 1.23 · 10 ^-3 7.71 · 10 ^-4 5.15 · 10 ^-3 2.23 · 10 ^-4 b ₄ 0 0 -2.11 · 10 ^-5 -8.3510 ^-7

The cleaned flue gas is emitted into the working area of the solid waste landfill.

The application of the proposed invention allows to ensure environmental safety and increase efficiency in the utilization of biogas by purifying exhaust gases by varying its composition through the use of preliminary purification of biogas, as well as evaluating combustion parameters and determining the approximate composition of emissions and adjusting the consumption of sorbents and reagent in the gas treatment system.

Claims (3)

1. A method of environmentally friendly thermal neutralization of biogas from solid waste landfills, including biogas extraction through drainage and forced creation of rarefaction, reduction of moisture content in extracted biogas due to a sharp decrease in temperature, biogas compression, preliminary biogas removal from moisture and hydrogen sulfide, dust removal from biogas filtration, biogas burning, cooling and purification of flue gases from acidic components and halogenated hydrocarbons, while in the stream flue gases continuously measure the concentration of hydrogen sulfide and acidic gaseous compounds of sulfur and carbon, taking into account which they dynamically adjust the consumption of sorbents and reagent based on approximating regression ratios obtained previously from experimental data. 2. The method according to claim 1, in which the biogas is cleaned from dust by filtration. 3. The method according to claim 1, in which the approximating regression relationships are as follows:

where
t is the temperature of the flue gases at any point in the gas cleaning tract;
c ₀ , c ₁ , c ₂ , c ₃ , c ₄ - constants of equation (1);
a ₀ , a ₁ , a ₂ , a ₃ - constants of equation (2);
b ₁ , b ₂ , b ₃ , b ₄ - constants of equation (3);
Ci is the concentration of the i-th pollutant in the flue gases at any point in the gas treatment path;
ΔP - rarefaction of flue gases at any point in the gas cleaning tract;
L is the distance from the origin to the point of definition of the parameter.