RU2069648C1 - Method of lime-stone processing - Google Patents

Abstract

FIELD: lime-stone burning field, method is used in production of building materials and carbon dioxide. SUBSTANCE: lime-stone comminution is made till fraction of 1 mm is no less than 90 %. Lime-stone clearing is exercised in gas flow of smoke gasses with separation of up to 90 % burned lime in cyclone. After cyclone smoke gasses are subjected to wet clearing with separation of lime milk and carbon dioxide. Gas flow is produced by fuel burning in oxidation medium made of mixture of after separation produced carbon dioxide and oxygen. EFFECT: increased effectiveness of lime-stone processing. 2 cl, 1 dwg

Description

 The invention relates to the field of calcination of limestone and can be used in the production of building materials and in the production of carbon dioxide.

A known method of calcining calcareous rock containing calcium carbonate to achieve a predetermined concentration of CO ₂ comprising calcining calcareous lime to produce lime-boiling with a given degree of calcination, purifying the exhaust gases from the furnace and supplying part of them in a mixture with cold air to cool the lime-boiling. The disadvantage of this method is the emission into the atmosphere of a significant amount of carbon dioxide and large heat loss [1]
Closest to the technical nature of the claimed invention is a method of processing limestone, including its grinding, firing in a gas boiler of air and fuel and purification of flue gases with separation in a cyclone of up to 90% of calcined lime [2]
The disadvantage of this method is the emission into the atmosphere of a significant amount of carbon dioxide and large heat loss.

 An object of the invention is to increase the utilization of raw materials, defined as the ratio of the mass of useful products to the total mass of raw materials, reducing heat loss and eliminating the emission of flue gases into the atmosphere.

 The problem is solved in that in the method of processing limestone, including its grinding, firing in a gas stream of air and fuel and purification of flue gases with separation in a cyclone of up to 90% of calcined lime, grinding is carried out to a fraction of 1 mm of not less than 90% and after cyclone smoke the gases are wet cleaned with the separation of milk of lime and carbon dioxide, while the gas stream is obtained by burning fuel in an oxidizing medium from a mixture obtained after separation of carbon dioxide and oxygen. In addition, carbon dioxide can be mixed with oxygen in a predetermined ratio.

The essence of the invention lies in the fact that the crushed limestone is calcined in a gas stream at a temperature of from 1250 to 800 ^o C. The temperature of the dust and gas stream after firing is reduced to 200 250 ^o C using a cooler, receiving steam pressure up to 10 MPa with a temperature of up to 150 ^o C. A gas stream is obtained by burning gaseous or liquid fuels in an oxidizing medium consisting of a mixture of oxygen and carbon dioxide. Thus, the dust and gas stream contains solid CaO particles, carbon dioxide and water vapor. Up to 90% of solid particles are separated from the dust and gas stream cooled to 200 250 ^° C and the residue is subjected to wet gas purification, separating from the gas stream up to 98% of the residue of calcined lime and most of the water vapor, thereby producing milk of lime and moist carbon dioxide. The established part of carbon dioxide is mixed with oxygen in a predetermined ratio to obtain an oxidizing mixture for combustion, and compressed, liquefied, or solid carbon dioxide are obtained from the carbon dioxide residue after drying and final purification. As a result, emissions of flue gases into the atmosphere are eliminated, while simultaneously reducing by 20 25% the heat loss from the exhaust gases. In addition to burnt lime, an additional product is obtained from limestone: carbon dioxide, increasing the utilization of raw materials to 85–90%. Milk of lime is used to deoxidize soils and to obtain alumina. Since the oxidizing agent contains CO ₂ as a ballast gas, only triatomic gases are contained in the flue gases and the radiant exchange is maximized, which increases the efficiency of heat recovery. The absence of an absorbent for producing carbon dioxide dramatically reduces the cost of the latter and reduces the size of the installation that implements the method.

 The drawing shows a block diagram of an installation that implements the method. The installation contains a ball mill 1 of dry grinding limestone, silo 2 for storing ground limestone, a decarbonizer-steam generator 3 with three inlets and three outlets, a cyclone 4 for separating CaO from flue gases, a compressor 5, a wet filter 6 with two inlets and two outlets, a mixer 7 with two inputs for the formation of an oxidizing mixture, an oxygen station 8, a limestone supply line 9, with pipelines 10, 11, 12, 13, 14 supplying an oxidizing agent, air, water to a decarbonizer-steam generator of DPG and water into a wet gas purification filter and fuel with Responsibly, the discharge pipes 14b, 15, 16, 17, 16a, 16b of steam sludge, calcined lime, milk of lime and carbon dioxide, respectively.

 The installation consists of conventional industrial equipment. DPG is implemented as a combustion chamber with cooling the walls of water, coupled with a tubular heat exchanger for cooling flue gases.

The limestone supply line 9 is connected through input 18 to mill 1, the output of which 19 is connected to input 20 of silo 2, and the output of the last 21 is connected to input 22 of DPG 3. Air supply pipe 11 through input 23 is connected to oxygen station 8, the output of which 24 is connected with the 25 input of the mixer 7. The output of the last 26 through the pipeline 10 is connected to the input 27 of the DPG 3. The fuel supply pipe 14a is connected to the same input. The water supply pipe 12 is connected to the inlet 28 of the DPG 3, and the output of the last 29 is connected to the steam discharge pipe 15. The outlet 30 of the DPG 3 is connected to the inlet 31 of the cyclone 4, the output of which 32 is connected to the CaO discharge pipe 16a. The output 33 of the cyclone 4 through the compressor 5 is connected to the input 34 of the filter 6 wet gas treatment. The inlet 35 of the latter is connected to the water supply pipe 13. The output 36 of the filter is connected to the pipe 17 of the discharge of CO ₂ and the input 38 of the mixer 7. Output 39 of the DPG 3 is connected to the pipe of the discharge of sludge 14b.

 The device operates as follows.

Limestone is fed through feed line 9 to input 18 of mill 1. From output 19 of the last, limestone, ground to 90% of 1.0 mm fractions, is fed to input 22 of DPG 3. Air through pipe 11 through input 23 is supplied to oxygen station 8, from the exit 24 which oxygen is fed to the inlet 25 of the mixer 7, in which it is mixed with CO ₂ in the ratio of 1 4 1 6. Through the outlet 26 of the mixer, the oxidizing agent containing 16 25% oxygen is fed through line 10 to the inlet 27 of the DPG 3. Fuel is also supplied there pipeline 14a. Chilled water is supplied through the inlet 28 from pipeline 12 to the DPG 3 at a temperature of from 20 to 80 ^° C. In the DPG 3, limestone powder is calcined at a temperature of from 800 to 1250 ^° C. It decomposes with the release of CO ₂ . Thus, the gaseous phase contains only triatomic gases CO ₂ and H ₂ O, which are formed during fuel combustion and decomposition of limestone. Undecomposed large particles (predominantly silicate impurities) are discharged via outlet 14b through outlet 39. Water vapor from outlet 29 of DPG 3 is discharged through line 15, and the dust and gas stream with CaO particles through outlet 30 at a temperature of 200 - 250 ^° C is fed to inlet 31 of cyclone 4, in which up to 90% of the solid phase is separated from the dust and gas stream. Calcined lime through the outlet 32 of the cyclone is discharged through the pipeline 16A. From the outlet 33 of the cyclone, the gas flow through the compressor 5 is fed to the inlet 34 of a wet gas filter 6, to the inlet of which 35 cold water is supplied. In the filter, water vapor from the flue gases condenses and quenches up to 98% of the CaO particles remaining in the stream to produce Ca (OH) ₂ . At the same time, all sulfur compounds are captured to form CaSO ₄ . The resulting milk of lime from outlet 36 is withdrawn via line 16b. From the outlet 37 of the filter 6, carbon dioxide at a temperature of up to 60 ^{° C. is} supplied to the inlet 38 of the mixer 7, and the remainder is removed through a pipe 17 for further use.

где G_т удельный расход топлива на 1 кг CaO.Usage example:
Limestone feedstock with water contents of 15% CaO 46% and CO ₂ 39% Fuel: fuel oil with a calorific value of 9500 kcal / kg. When burning 1 kg of fuel oil in an oxidizing medium containing 20% oxygen and 80% CO _2, it is necessary to spend 2.26 m ³ / kg of oxygen with an oxidizing agent consumption of 11.29 m ³ / kg. In this case, flue gases are obtained with a content of 10.62 m ³ / kg CO ₂ 1.34 m ³ / kg water vapor. Out of 10.62 m ³ / kg of carbon dioxide, 9.03 is circulating gas, a mixer circulating in a closed circuit, a cyclone gas generator, a compressor, a filter and a mixer. The total composition of the products of combustion and decomposition of limestone per 1 kg of CaO (i.e., 2.18 kg of limestone) is determined by the formula

where G _t specific fuel consumption per 1 kg of CaO.

V ₁ , V ₂ output of CO ₂ and H ₂ O when burning 1 kg of fuel oil,
γ ₁ , γ ₂ specific gravities of CO ₂ and H ₂ O, respectively,
C ₁ and C ₂ content of CO ₂ and H ₂ O in limestone in fractions.

где 675 тепло в ккал/кг, затрачиваемое на нагрев и испарение воды, содержащейся в известняке,
2,18 количество известняка, необходимое для получения 1 кг СаO,
ТС теплотворная способность топлива,
S_и, S₁, S₂ удельные теплоемкости известняка CO₂ и H₂O соответственно.We divide the DPG into three zones: in the first, the combustion of fuel in an oxidizing medium occurs. In this case, the temperature of the limestone and flue gases rises to T degrees and the moisture of the limestone evaporates. In the second zone, limestone decomposes and the temperature of the gases decreases to 800 ^o C. In the third zone, the temperature of the exhaust gases decreases to 200 ^o C due to heat recovery in the convective surface. Thus, all the heat introduced by the fuel, limestone at temperature T _{and the} return gas at temperature T _in is consumed in the first zone to produce a certain amount of steam G ₁ , the evaporation of limestone water and heating of the components to temperature T. The heat balance equation for this zone has the form

where 675 heat in kcal / kg spent on heating and evaporation of water contained in limestone,
2.18 the amount of limestone required to obtain 1 kg of CaO,
TS calorific value of fuel,
S _and , S ₁ , S ₂ specific heat capacity of limestone CO ₂ and H ₂ O, respectively.

In the second zone in the temperature range from T to 800 ^o C the heat balance equation has the form.

где 350 тепло на разложение 1 кг известняка в ккал/кг.

where 350 is the heat of decomposition of 1 kg of limestone in kcal / kg.

G ₂ heat to generate steam in the second zone.

где G₃ тепло на нагрев и испарение воды.In the third zone, the heat balance has the form

where G _{3 is} heat for heating and evaporation of water.

Thus, the total heat to receive steam in all three zones is
QG ₁ + G ₂ + G ₃
The amount of steam generated per 1 kg of CaO is equal to:
C _p Q / I (6)
where I is the enthalpy of steam generated.

The oxygen consumption for burning 1 kg of fuel oil is
V _to 0.0187C ^p + 0.056 H ^p
where C ^p is 84.8 and p ^p is 12.

The mass flow rate of oxygen is
C ^k = γ ₃ • V _k • G _t (7)
where γ _{3 is the} specific gravity of oxygen. At a 20% oxygen content in the oxidizing agent, the consumption of the latter for burning 1 kg of fuel is
V _o V _to • 5
The return of carbon dioxide in the DPG is
V _to V _o Y _to
The weight return of carbon dioxide is
G _c = γ ₁ • G _t • V _in
The commercial yield of carbon dioxide is:
G _st = V ₁ • G _t • γ ₁ + C ₁ • 2,18-G _c
The cost of oxygen for the production of 1 ton of CaO is equal to:
C ₁ C _to • C _to
where C is _the cost of one ton of oxygen. The cost of carbon dioxide is
C ₂ G _s • C _c
where C _{c is the} cost of one ton of carbon dioxide. With a specific consumption of electric energy E for grinding 1 ton of limestone and at a cost of 1 kWh of electric energy C _{e, the} consumption for grinding is
C ₃ 2.18 • E • C _e
Profit from the sale of carbon dioxide will be:
P C ₂ C ₁ C ₃
We define the main process parameters at: S _and 0.28 kcal / kg • ^o C, S ₁ 0.436 kcal / kg • ^o C, S ₂ 0.366 kcal / kg • ^o C, TC 9500 kcal / kg, T _and 20 ^o C, T _at 60 ^o C, C ₁ 0.39, C ₂ 0.15, γ ₁ 1.977 g / cm ³ , γ ₂ 0.805 g / cm ³ , γ ₃ 1.429 g / cm ³ , V ₁ 10.62 m ³ / kg, V ₂ 1.34 m ³ / kg, I 695 kcal / kg, C _to 90,000 rubles / t. C _c 75,000 rubles / t, C _e 12 rubles / kWh, E 40 kWh / t.

In accordance with (1), we obtain V _c 10.62C _t + 0.425 and V _n 344G _t + 0.406. In accordance with (2) at T 1200 ^o C and G ₁ 10 kcal / kg, we obtain C _t 0.28 kg / kg. In accordance with (3), we obtain, after data substitution, G ₂ 227 kcal / kg. According to (4), after data substitution, we obtain G ₃ 1240 kcal / kg. In accordance with (5), the total heat consumption for steam production is 1477 kcal / kg. In accordance with (6), the total weight of the steam produced in the steam generator without taking into account environmental losses is 2.12 kg / kg. In accordance with (6), the oxygen consumption for burning 1 kg of fuel oil is 2.258 m ³ / kg, the weight oxygen consumption in accordance with (7) is 0.9 kg / kg. The return of carbon dioxide to DPG and the oxidizer consumption for the production of 1 ton of CaO in accordance with (8) and (9) are V _o 2.258 • 5 11.29 m ³ / kg and V _at 11.29 2.258 9.032 m ³ / kg. The return of carbon dioxide by weight and in accordance with (10) is 5.05 kg / kg. Commodity yield of CO ₂ is equal to 1.68 kg / kg in accordance with (11). In accordance with (12), the cost of oxygen to obtain t. CaO is 81,000 rubles. In accordance with (13), the cost of marketable carbon dioxide is 126,000 rubles. In accordance with (14), the cost of electricity for grinding 2.18 tons of limestone is 1000 rubles. In accordance with (15), the profit from the sale of carbon dioxide is 44,000 rubles / t.

In accordance with (1), the total volume of water vapor in flue gases is 0.784 m ³ / kg or in weight units 0.636 kg / kg, which makes it possible to obtain 636 kg of milk of lime with 157 g / l of active oxide per 1 ton of burnt lime calcium at 100% wet flue gas cleaning efficiency and 90% dry cleaning efficiency

Claims (2)

 1. A method of processing limestone, including its grinding, firing in a gas stream of air and fuel and purification of flue gases with separation in a cyclone of up to 90% of calcined lime, characterized in that the grinding of limestone is carried out to a fraction of 1 mm of not less than 90% and after cyclone flue gases are subjected to wet cleaning with the separation of milk of lime and carbon dioxide, while the gas stream is obtained by burning fuel in an oxidizing medium from a mixture obtained after separation of carbon dioxide and oxygen.  2. The method according to claim 1, characterized in that the carbon dioxide is mixed with oxygen in a predetermined ratio.