JPS59157420A - Combustion controlling method utilizing mixed gas fuel - Google Patents

Abstract

PURPOSE:To prevent the thermal data of a thermal installation from fluctuation, also contrive the energy-saving and low cost by a method wherein a pure oxygen is introduced into a combustion air line under the control of supplying quantity thereof according to the fluctuation of calorific value produced from mixed gas. CONSTITUTION:A first calculator 11 calculates the optimum oxygen density for an objective heating furnace 1 with collating to the relation shown in previously known figure based on the actual calorific value of a mixed gas fuel 3 from a calorimeter 7. Subsequently, the second calculator 12 calculates required amount of air and pure oxygen based on the optimum oxygen density from the first calcultor 11, and theoretical amount of air from A0 meter 8, then outputs those data to a comparative calculator 13. The comparative calculator 13 decides the ratio of said data, then the optimum oxygen density condition can be regulated by controlling for each amount of pure oxygen and combustion air. The controlling of said oxygen and air is actually performed with flow regulators 5C, 4C, hereupon, the density value from a density meter 9 is compensated in a density compensating circuit 3D.

Description

DETAILED DESCRIPTION OF THE INVENTION Conventionally, in steel works, when by-product gas within the plant is burned as fuel, various types of fuels have been mixed and fed to a heating furnace or the like. When performing combustion control using fuels with different calorific values, the Wobbe Index (Wobbe 4n
This is supported by dex) control, theoretical air volume (AO) control, etc.

However, if the calorific value of the mixed gas fluctuates greatly over time, the heat transfer performance from the flame and combustion gas to the material changes greatly. In addition to causing inconvenience in the important thermal equipment, the unit heat consumption also fluctuates significantly.

To deal with this, enriching the combustion air with pure oxygen is an effective means to maintain the same gas temperature and heat unit regardless of changes in the calorific value of the mixed gas. Combustion by enriching pure oxygen itself is not necessarily new, but is known, for example, from Japanese Patent Laid-Open No. 57-41521.

However, in the past, generally5, oxygen enrichment to combustion air was performed at a constant pure oxygen input rate, in other words, the oxygen concentration after enrichment was constant, and as in the method of the present invention, the heating value of the fuel was The purpose of the present invention is to prevent wide fluctuations in the thermal specifications of thermal equipment, such as the gas temperature distribution in the furnace and the unit heat consumption. However, it is an object of the present invention to provide a combustion control method that can appropriately respond to variations in the calorific value of the mixed gas fuel used.

The key point of the present invention is that in a combustion system that uses a mixture of two or more gaseous fuels having different calorific values, the calorific value of the mixed gas is detected, and this is calculated from the previously known fuel calorific value. The method uses a mixed gas fuel characterized by determining the optimal amount of oxygen by comparing the relationship between Combustion control method, Nichiru.

As mentioned above, in a steelworks, the byproduct gases listed in the table below are supplied to a large number of thermal equipment within the factory, but depending on the operating status of the source of the byproduct gas and the operating status of each heating equipment,
The gas generation and usage conditions change from time to time, and the gas flow inside the factory changes.Despite these circumstances, if the oxygen enrichment rate is kept constant as in the conventional example, the gas If a surplus exceeds the capacity of the holder, the gas must be dissipated at all costs, and if a shortage occurs, the amount of fuel purchased from outside, such as LPG, must be increased.As a result, By-product gas cannot be used to the maximum extent, which poses a problem from the point of view of energy conservation.By the way, when mixed gas f is enriched with oxygen, even if it is low-calorie, it becomes equivalent to high-calorie gas. The inventor obtained the results shown in Fig. 1 through various experiments. This study investigated the relationship between the calorific value and the oxygen enrichment rate to make it equivalent to coke oven gas (COG).

Therefore, if such a relationship is determined in advance, for example, when using a mixed gas (B, CM) of BFG and COG, even if BFG and COG vary, it will be possible to adjust the relationship according to the current calorific value of the mixed gas. By controlling the amount of pure oxygen to adjust the oxygen enrichment rate, it is possible to always maintain a combustion state equivalent to combustion with COG alone, thereby constantly maintaining the heat transfer performance to the material, the gas temperature distribution in the furnace, the unit heat consumption, etc. Can be held constant.

The present invention is based on the above-mentioned concept, and the dog contributes to the effective use of thermal energy. However, if the price of pure oxygen is high, there is no advantage in applying the method of the present invention, but in reality, the price of pure oxygen is not that high.

Note that "pure oxygen" does not necessarily mean that 0.2% is 1ooq6
It doesn't have to be that high; in extreme terms, it just needs to be higher than the oxygen concentration in the air.

The present invention will be described in more detail below with reference to a specific example shown in FIG. 2. Reference numeral 01 is a heating furnace as an example of thermal equipment, and a burner 2 attached thereto is provided with a supply system for mixed gas fuel 3 and combustion air 4. In the present invention, a supply system for pure oxygen 5 is added. Each supply system has flowmeters 3Q, 4Q, 5
Q, flow rate controllers 3C, 40, 5C and flow rate control valves 3V, 4V for adjusting the flow rate in response to the flow rate signal;
5V is provided for each.

In addition, the supply system of the mixed gas fuel 3 includes a density correction circuit 3D.
are arranged.

Further, a detector 6 is provided in the supply path of the barber gas fuel 3, and the detection signal is transmitted from a calorimeter 7, Ao (theoretical air amount) total 8,
The signals from these meters 7, 8.9 are processed as follows in the direct digital control (CDDC) control system 10. Based on the current calorific value of the mixed gas fuel 3 from 7, the first computing unit 11 refers to the previously known relationship shown in FIG. 1 to determine the optimum oxygen concentration for the target heating furnace 1. For example, when the mixed gas is BCM,
If the current calorific value is 2750 krO11t/N m:', then from the relationship in Figure 1, the optimum oxygen concentration is 24
．． 4%.

Next, the second calculator 12 calculates the ratio based on the optimal oxygen concentration from the first calculator 11 and the theoretical air amount from the Ao meter 8 to calculate the required air amount and pure oxygen amount. Arithmetic unit 13
Output to. The ratio calculator 13 determines the ratio.0 To explain this numerically, from the current theoretical air amount, based on the 21st oxygen-containing air standard, the amount is 2.42 m per fuel IN'.
/i'Jm? If it is determined that this air is necessary, then a process is performed to correct Ao to AO' so that the oxygen concentration becomes the aforementioned optimum oxygen concentration of 24.4%. −
! Based on the 21st standard oxygen-containing air, in air of 2.42Ni, approximately oxygen is 0,51 (= 2.42X0.21
)Nm', nitrogen is approximately 1.91 (=2.42X0.79
) Nm” ○ Therefore, Ao' is 0.5110.2.i
4=2. It is fixed as lNm3. Therefore, if XNm3 of pure oxygen and yNrrl of combustion air are supplied, the following simultaneous equations hold true.

By solving this, you can find x and y, and conversely, by controlling the amount of pure oxygen, 1, and the amount of combustion air, respectively, so that X + y, you can adjust to the optimal oxygen concentration state. Then, adjust the flow rate. A total of 5C and 4C actually perform the control. Here, the density value from the density meter 9 is corrected in the density correction circuit 3D and taken into the flow rate controller 30 because the density of the mixed gas fuel is adjusted to the amount of each gas as shown in the above table. This is because the value of the flow meter 3Q cannot be used as is because it varies widely depending on fluctuations in the flow rate.

On the other hand, such control takes the form schematically shown in FIG. 3. In other words, initially (1) CO'G was burned alone, but as the amount decreased, 13FG was added.However, adding BFG alone would change the thermal specifications in the heating furnace, so pure oxygen was burned. is added (■), and the BFG amount and 02 amount are subsequently controlled according to changes in the COG amount. Incidentally, in FIG. 3, fluctuations in the combustion air are omitted.

Therefore, if COG is running low and B'FG is in surplus, temperature fluctuations in the furnace can be prevented by simply adding pure oxygen, as shown in process (b). Eliminates the need to purchase external fuel, which is more expensive than pure oxygen.

As described above, since the present invention injects pure oxygen into the combustion air system while controlling its amount in accordance with the fluctuations in the calorific value of the mixed gas, fluctuations in the thermal specifications of the thermal equipment can be avoided. Not only can this be prevented, but it is also possible to make maximum use of by-product gas in factories where gas balance tends to collapse, which greatly contributes to achieving energy savings and lower costs.

[Brief explanation of the drawing]

Fig. 1 is a correlation diagram showing the optimum oxygen concentration corresponding to the calorific value of mixed gas fuel, Fig. 2 is a flow chart showing the control method of the present invention, and Fig. 3 is an explanatory diagram showing an example of a control example. be.

Claims (1)

[Claims] (1) In a combustion system that uses a mixture of two or more gaseous fuels that have at least different calorific values, the calorific value of the mixed gas is detected, and this is used to calculate the relationship between the known fuel calorific value and the optimal amount of oxygen. A combustion control method using a mixed gas fuel, characterized in that the optimum amount of oxygen is determined by comparing the amount of oxygen to the combustion air system, and pure oxygen is injected into the combustion air system while controlling the amount so as to reach the optimum amount of oxygen.