JPH0327500B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas circulation type lime calcination device for calcination of quicklime from limestone. The present invention relates to an exhaust gas circulation type lime sintering device capable of sintering quicklime.

Quicklime (CaO) is calcined based on the reaction shown in equation (1) below, that is, by heating to about 820° C. to separate carbon dioxide (CO ₂ ) from limestone (CaCO ₃ ).

CaCO ₃ →CaO+CO ₂ -43Kcal...(1) Conventionally, an exhaust gas circulation type kiln has been used as a device for baking such quicklime. In the exhaust gas circulation type kiln, the outer periphery of the raw stone storage part through which limestone, which is the raw stone for quicklime firing, is allowed to descend and pass through is configured with a lattice, and the fuel is stored in the combustion chamber formed on the outer periphery of the lower part of the raw rock storage part. After the combustion gas obtained by burning the limestone is detoured to the opposite side of the burner installation position, it is guided into the raw stone storage section, and is passed across the inside of the raw stone storage section to contribute to the heating of the limestone passing through it. A part of the combustion exhaust gas that has come out of the raw ore storage area is guided to the outside of the storage area by the flow of auxiliary combustion air that is discharged from the ejector nozzle into the diff user at a constant discharge pressure (approximately 4000mmH ₂ O). The fuel is sucked in and guided into the combustion chamber by the diffuser, thereby being circulated.

As the fuel, a low-calorie gas can also be used since the burning of quicklime is carried out based on convection heat transfer as described above. Therefore, in response to the recent energy situation, we replaced conventional heavy oil with blast furnace gas (BFG).
Attempts are being made to switch to low-calorie gases such as However, burning such a low-calorie gas alone should be avoided because of the narrow flammability range, low flame temperature, and unstable ignition. Therefore, it is considered to use a gas mixed with coke gas (COG) etc. (hereinafter referred to as M gas), but when using M gas, the gas radiation will be lower than that of heavy oil, and the flame temperature will be lower. M gas cannot be used as it is as a fuel in conventional firing furnaces designed and manufactured for heavy oil, for reasons such as lower production efficiency due to lower production efficiency.

As a countermeasure for the above-mentioned problem, the applicant has found that it is effective to control the air ratio and circulating gas ratio (the ratio of the amount of combustion exhaust gas to be circulated and the amount of auxiliary combustion air) according to the unit calorific value of the fuel. I found out. The present invention was made based on such knowledge,
The present invention provides an exhaust gas circulation type lime sintering device that burns quicklime without reducing productivity while switching from conventional heavy oil to low-calorie gas of 2000 Kcal/Nm ³ or less as fuel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The lime calcining apparatus according to the present invention will be described in detail below based on drawings showing embodiments thereof.

Reference numeral 11 denotes a raw stone storage part constituting the central part of the lime kiln 1, which is arranged vertically and has a prismatic lattice 11.
Its outer periphery is constituted by a. A mortar-shaped hopper 12 is connected to its upper end, and a chute 13 having a discharge port opening onto the conveyor 2 is connected to its lower end. The rough stone storage portion 11 has penetrating portions 14a and 14b formed at the upper and lower center to connect the hopper 12 and the chute 13,
The surrounding area is covered with a furnace shell 14 made of a heat-resistant material. The inner diameter of the furnace outer shell 14 is designed to be larger than the outer diameter of the raw ore storage section 11 by a predetermined dimension, and a gas flow space 15 is formed between the two.

The lower part of the gas flow space 15 corresponds to a combustion chamber 15a, and a burner 3 capable of burning gas fuel at a low air ratio is attached to the combustion chamber 15a. That is, at the bottom of the furnace shell 14, there is a flow control valve 3.
1a and orifice flow meter 31b are arranged in the middle of the pipe, and gas fuel (M gas with calorific value of 1870 Kcal/Nm ³ ) is placed in the middle of the pipe.
A fuel supply pipe 31 and a flow control valve 32 that supply
The burner 3, which is connected to an air supply pipe 32 which supplies main auxiliary combustion air, is installed with its outlet facing into the furnace. Then, fuel is supplied through a fuel supply pipe 31 and air supply pipe 32
The main auxiliary combustion air supplied in the combustion chamber 15a is mixed in the burner 3, and the auxiliary auxiliary combustion air, which will be described later, is also added and combusted in the combustion chamber 15a to generate combustion gas.

In addition, in the part of the rough stone storage part 11 that is directly hit by the flame of the combustion gas, a closed peripheral wall 11b is attached instead of the grid 11a.
The flame of the burning gas is prevented from entering directly into the raw stone storage section 11.

Furthermore, a cylindrical diff user 5 is arranged above the burner 3 mounting position in the gas flow space 15, and a pressure gauge 4b is arranged in the middle of the pipe at the upper opening of the diff user 5 to supply air. A nozzle 4a of an ejector 4 connected to an air supply pipe 41 is inserted, and its lower opening is located immediately above the burner 3. A part of the combustion exhaust gas flows into the auxiliary auxiliary combustion air discharged from the nozzle 4a of the ejector 4 (indicated by a broken line arrow in the figure).
The fuel is sucked in by the diffuser 5 and guided into the combustion chamber 15a for circulation.

The hopper 12 and the chute 13 are also provided with exhaust gas discharge ports 6 and 7 for guiding combustion exhaust gas out of the furnace. The exhaust gas exhaust ports 6 and 7 are connected to an exhaust gas exhaust pipe 61 having an orifice flow meter 61a disposed in the middle of the pipe, and an exhaust gas exhaust pipe 71 led into the heat exchanger 8, respectively. The exhaust gas exhaust pipe 71 is connected to the exhaust gas exhaust pipe 61 through a piping system within the heat exchanger 8 for preheating the air drawn in by the blower 81 to produce the auxiliary combustion air. The air supply pipe 82 that supplies the air to be preheated by the heat exchanger 8 has a thermometer 82a, a flow rate control valve 82b, and an orifice flowmeter 82c arranged in the middle of the pipe, and the end of the pipe supplies auxiliary air. It is connected to the air supply pipes 32 and 41 for supply.

Note that the above-mentioned orifice flowmeters 31b, 61
82c, thermometer 82a, etc., a combustion chamber 15a is installed at an appropriate position in the gas flow space 15 between the raw ore storage section 11 and the furnace shell 14 as a sensor for obtaining data for control. Thermometer 15b to measure the temperature and concentration of O ₂ gas (or CO gas)
and a gas analyzer 15c, a thermometer 4c near the nozzle 4a of the ejector 4 to measure the temperature of the flue gas being circulated, and a thermometer 4c located at an appropriate position in the hopper 12 to measure the temperature of the flue gas being discharged. Thermometers 12a are respectively arranged for measurement. All measurement data from these sensors is input to the arithmetic and control unit 9. Furthermore, data such as the circulating gas ratio r, air ratio m, theoretical air flow rate per unit amount of fuel A _{0 , theoretical gas flow rate G 0} , calorific value HL, etc. set by the setting device ₁₀ are also input to the arithmetic and control unit 9. Meanwhile, the control signals calculated there are output to the flow rate regulating valves 31a, 32a, and 82b.

Next, the reason why it is possible to convert heavy oil to gas fuel by using the apparatus of the present invention having such a configuration will be explained. Converting fuel without changing productivity means keeping the fuel consumption rate constant before and after the conversion, which means keeping the temperature and flow rate of combustion gas constant.

Now, if the temperature and specific heat at each position in the furnace of the lime calcining equipment are constant, the following equation (2) holds true from the standpoint of heat balance.

Q _Io +Q _A +Q _R =Q _CaO +Q _R +Q _W …(2) However, Q _Io : Sensible heat of supplied fuel Q _A : Sensible heat of auxiliary combustion air Q _R : Sensible heat of circulated combustion exhaust gas Q _CaO : Heat of lime formation Q _W : Sensible heat of combustion gas discharged from exhaust gas exhaust pipe 7 Also, from the exhaust gas balance, the following equation (3) holds true.

{(m-1)A ₀ +G ₀ }Q _Io /Hl+GR+GCO ₂ =G _R +G _W …(3) However, m: Air ratio A ₀ : Theoretical air flow rate G ₀ : Theoretical exhaust gas flow rate Hl: Calorific value G _R : Flow rate of circulating combustion exhaust gas G _CO2 : Flow rate of carbon dioxide gas GW: Flow rate of combustion gas discharged from exhaust gas discharge pipes 6 and 7 Furthermore, when converting fuel from heavy oil to M gas, the fuel consumption rate is kept constant. In order to do so, it is necessary to satisfy the following equation (4) derived from the above equations (2) and (3).

{(m−1)A ₀ +G ₀ }Q _Io /Hl = {m′−1)A′ ₀ +G′ ₀ }Q _Io /Hl′ …(4) However, without a dash (′): In the case of heavy oil firing With dash ('): In the case of M gas firing In other words, the air ratio may be changed according to the unit calorific value of the fuel. However, when changing the air ratio, it is necessary to change the flow rate of the auxiliary combustion air. When changing the auxiliary combustion air flow rate, it is necessary to change the circulating gas ratio r shown in equation (5).

r=G _R /A ₃ (5) However, G _R : Flow rate of the circulated combustion exhaust gas A ₃ : Flow rate of the auxiliary combustion air In other words, it is also necessary to control the circulating gas ratio r.

The circulating gas ratio r is controlled by adjusting the valve opening of the flow rate control valve 32a while measuring with the pressure gauge 4b, and controlling the supply amount of the main auxiliary combustion air directly supplied to the burner 3 through the air supply pipe 32. This is done by indirectly adjusting the amount of auxiliary combustion air supplied by the air supply pipe 41 and controlling the air discharge pressure from the nozzle 4a of the ejector 4. In addition,
Control can also be achieved by changing the diameter of the nozzle 4a of the ejector 4. Further, the air supply pipe 41 may be provided with a flow rate control valve.

Next, the control contents of the arithmetic and control unit 9 will be explained.

First, the required fuel supply amount is calculated based on the furnace temperature and exhaust gas temperature measurement data from the thermometers 4c, 12a, and 15b, and in order to achieve this, the flow control valve 31a uses the measurement data from the orifice flowmeter 31b as a feedback signal. The amount of fuel supplied is controlled so that the temperature inside the furnace reaches a predetermined temperature by adjusting the opening of the furnace.

Next, an auxiliary combustion air amount corresponding to the above fuel supply amount is calculated. This is calculated by multiplying the fuel supply amount, the theoretical air flow rate per unit _A0 , and the air ratio m by the gas analyzer 15
It is obtained by adding the amount determined by the amount of O ₂ gas in the combustion gas measured in step c. The amount of auxiliary combustion air is controlled by the orifice flow meter 82c based on this calculation result.
This is done by adjusting the opening degree of the flow rate control valve 82b using this as a feedback signal.

The fuel supplied to the burner 3 and the auxiliary combustion air preheated by the heat exchanger 8 are mixed in the burner 3 and combusted in the combustion chamber 15a, but the resulting combustion gas is As shown by the arrow in the middle, after detouring to the gas flow space 15 on the opposite side of the burner 3 installation position, the grid 11a is inserted into the ore storage part 11.
guided inward. The combustion gas is then transferred to the raw stone storage section 1.
After contributing to the heating of the limestone passing through the limestone 1 and descending therein, a part of the limestone is led to the gas flow space 15 on the side where the burner 3 is attached and becomes combustion exhaust gas. This combustion exhaust gas is sucked into the flow of auxiliary combustion air generated by discharging the auxiliary combustion air that entered the air supply pipe 41 from the air supply pipe 82 into the diff user 5 from the nozzle 4a of the ejector 4, and is further sucked into the flow of auxiliary combustion air that is generated by the combustion air that has entered the air supply pipe 41 from the air supply pipe 82. It is guided to the air outlet and circulated.

The circulating gas ratio is determined by this sub-auxiliary combustion air amount, and the arithmetic and control unit 9 controls the set circulating gas ratio r.
The amount of auxiliary auxiliary combustion air required to achieve this is calculated, and the main auxiliary combustion air flows through the air supply pipe 32 so that this amount of air flows through the air supply pipe 41 and the ejector 4.
The opening degree of the flow rate control valve 32a is adjusted.

By circulating the exhaust gas in this way, it is possible to maintain a constant gas concentration in the furnace and to maximize thermal efficiency, making it possible to use low-calorie gas as fuel without reducing productivity. It becomes possible to burn quicklime.

In addition, data regarding the concentration of O ₂ gas in the combustion gas is obtained from the gas analyzer 1 near the combustion chamber 15a.
5c was used, but it is also possible to use a measurement near the nozzle 4a of the ejector 4. In addition, gas other than the combustion exhaust gas that is circulated as described above can be directly discharged from the exhaust gas outlet 6 via the exhaust gas exhaust pipe 61 to the outside of the furnace, or the exhaust gas can be directly discharged from the exhaust gas outlet 7 via the exhaust gas exhaust pipe 71 to the combustion air. As is conventional, the heat is fed into the heat exchanger 8 for preheating and then discharged to the outside of the furnace for treatment.

As detailed above, the lime sintering apparatus according to the present invention includes means for changing the amount of main auxiliary combustion air and the amount of auxiliary auxiliary combustion air, a burner that can combust combustion gas at a low air ratio, and a control device thereof. Therefore, the air ratio and circulating gas ratio can be controlled according to the unit calorific value of the fuel, and quicklime can be fired without reducing productivity even though low calorie gas is used as the fuel.

[Brief explanation of drawings]

The drawings are schematic diagrams showing embodiments of the present invention. 1... Lime firing furnace, 11... Raw stone storage section, 11a...
Grating, 14...Furnace shell, 15a...Combustion chamber, 2...Conveyor, 3...Burner, 4...Ejector, 4a...Nozzle, 5...Diffuser, 8...Heat exchanger, 9...Arithmetic control unit, 10...Setter.

Claims (1)

[Claims] 1 Exhaust gas circulation type lime that supplies combustion gas to the raw stone storage area in the furnace and heats it, and circulates a part of the heated combustion exhaust gas to the combustion chamber along with the auxiliary combustion air that is blown into the furnace from the ejector. A firing furnace,
It is equipped with an air supply amount adjustment valve to the ejector and a main auxiliary combustion air amount adjustment valve supplied to the burner section of the lime kiln, and further includes a control valve according to the unit calorific value of the gas fuel in order to make the fuel consumption rate a predetermined value. 1. A lime sintering apparatus characterized by comprising a device for controlling the opening degrees of both of the control valves so as to achieve an air ratio defined by the above and a ratio between an amount of circulating combustion exhaust gas and an amount of auxiliary auxiliary combustion air.