JPS60202716A - Method for controlling injecting rate of nh3 in noncatalytic denitrating method - Google Patents

Abstract

PURPOSE:To perform adequate injection of NH3 in a noncatalytic denitration method by measuring the temp. of a reaction space as well as the concn. of NOx after denitration and the amt. of waste gas by predicting the amt. of the NOx to be generated and the concn. of leak NH3 and controlling the injecting rate of NH3 according thereto. CONSTITUTION:The past injecting rate of NOx and NH3 is initially set and the temp. of the waste gas in a reaction space and the amt. of the waste gas are measured. The NOx after denitration is measured and the predicted amt. of NOx is calculated. On the other hand, whether the amt. of the NOx at certain time is within the permissible difference of the target value or not is checked from the DELTAt obtd. by dividing specified time by L and the integrated value of the NOx. Whether the incremental amt. of the NOx in the time DELTAt is within the permissible value of the target value or not is checked. Leak NH3 is calculated from the present time T and NH3/NOx ratio and whether said NH3 is smaller than E or not is checked. Whether the injecting rate of the NH3 is smaller than a set value M or not is also checked. When the leak NH3 is larger than E, the NOx target value is set and changed to a slightly higher value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the amount of NH3 injection using a non-catalytic denitrification method.

The non-catalytic denitrification method is a method in which NHa is added to the reaction space to convert NOx in the exhaust gas into water and nitrogen, making it harmless.
This method has been proposed by the applicant in Japanese Patent Publication No. 50-23664 and the like. In this method, it is important to control the amount of NH3 injected into the reaction space.
There is a risk of leaking and causing secondary pollution, and if it is too low, there is a problem that sufficient denitrification cannot be performed.

Therefore, various methods for controlling the amount of NH injection have been proposed and implemented.

One of the methods is to first predict the amount of NOx generated from the incinerator's process data (incineration amount, combustion air flow rate, temperature, exhaust gas flow rate, temperature, etc.) and then set the NOx amount at an appropriate NH3/'NOx ratio.
A method for controlling a large amount of Ha injection is known.

The configuration of this method is shown in FIG. 1(A). In the figure, (1) is a furnace, (2) is a reaction space, (3) is an NH3 source, (4) is a control valve, (6) is a calculation device, and (7) is process data.

However, with this method, during fluctuations in the amount of NOx generated,
~200 ppm, which may deviate greatly from the results predicted from the process data, in which case there may be excess NH3.
state, its excess NH.

The disadvantage is that ammonium chloride and ammonium sulfate adhere to equipment after the reactor, causing corrosion and blockage. Ammonium chloride and ammonium sulfate that did not adhere are fume-like and submicron dust (particle size of 1 μm or less), so they are not collected by electrostatic precipitators and are not discharged from chimneys.
Then it becomes white smoke. Also, if the amount of NH3 injection is small, NOx
This means that it will not be possible to meet the emission regulation values.

Next, as shown in FIG. 1 (CB), a NOx measuring device (5) is used before the NHs injection position. A method is known in which the NoX concentration is measured and the amount of NH and injection is proportionally controlled in accordance with the fluctuation thereof.

In this method, when there are large fluctuations in NOx concentration, such as in a garbage incinerator, the response tends to be delayed, and there is a problem similar to that described above. Furthermore, since the exhaust gas at the sampling point is high in temperature and has a high concentration of sulfur, analytical troubles such as failure of the analyzer due to packing of the sampling tube occur, and there are drawbacks such as the inability to control the appropriate amount of NH3 injection.

Furthermore, as shown in Figure 1 (C) K, NOx after the denitration equipment
There is a method of measuring the concentration and controlling the amount of NHs injection so that the NOx emission regulation value can be cleared.

In this case, in addition to the same problems as the above two methods, NI
(Note 3) There is a drawback that an excessive amount of N)I3 is injected due to the influence of the concentration at the peak of NOx generation. Further, if the reaction space temperature deviates significantly from the non-catalyst optimum temperature of 800 to 900°C, the denitrification rate decreases. For this reason, the method of controlling large amounts of N)I3 injection has the disadvantage that when the reaction space temperature deviates from the optimum temperature and the denitrification rate decreases, it becomes uncontrollable and an excessive amount of nitrate is injected.

The present invention was made to improve the drawbacks of these conventional methods, and measures the reaction space temperature and NOx concentration after denitrification,
Furthermore, the basic feature is that the amount of exhaust gas after denitrification is calculated or measured, the amount of NOx generated and the leaked NH3 concentration are estimated from these values, and the amount of NH and injection into the reaction space is controlled based on the predicted values. That is.

The method of the present invention will be explained step by step with reference to the conceptual diagram of FIG. 2 and the flowchart of FIG. 3. Note that the numbers in the flowchart of FIG. 3 correspond to the following steps.

■Initialize past NOX 1NH3 injection amount.

1. When driving for the first time. Expected NOx generation amount and NH3 injection f
lkv+- initialize.

(2) Measure the exhaust gas temperature and exhaust gas amount tl in the reaction space. The amount of exhaust gas is measured at the location where the NOx measuring device (5) is installed. Note that exhaust gas I is from an incinerator, boiler (or gas cooler)
It may also be calculated by a heat balance calculation using as one system.

■Measure NOx after denitrification.

■Calculate the expected NOx generation amount. This NOx generation amount calculation method is shown in FIGS. 4 and 5.

■As shown in Figure 6, Δt and ΔN are obtained by dividing a certain period of time into L equal parts.
The integrated value of Ox is used to check whether the amount of NOx at a certain time is within the tolerance of the target value.

In the figure, A: Arbitrary setting of the allowable upper limit value from the target value B: Arbitrary setting of the lower limit value for a certain period of time.

■If the current ΣNOX/ΣΔt is larger than the upper limit value, then NH
, increase the injection volume by 1 to increase the denitrification efficiency and keep it within the upper limit.

n: NH, injection amount increase ratio, arbitrary setting ■Current Σ
If NOX/ΣΔt is smaller than the lower limit, NH3 injection amount t
Multiply by m to lower the denitrification efficiency and reduce NH3 consumption so that it falls within the lower limit.

m: NHs injection amount/large/small ratio, arbitrary setting ■ Check whether the amount of increase in NOX is within the tolerance of the target value based on Δ shown in Fig. 7 over time.

C in the figure: target upper limit value A/LXc, optionally set target lower limit value B/LXds.

■ If Δ is the NOx increase amount over time ΔNOx is larger than the upper limit value, then the large amount of NHa injection is multiplied by the result of ■ [Stock] Δ is the NOx increase I amount over time ΔNOx is smaller than the lower limit value, then the large amount of NHs injection Multiply the result of large quantity ■ by m.

■Leak NH, = f (T-NH3/NOX ratio) (8th
Check if it is less than EJt).

E: Secondary pollution occurrence limit value, initial setting value @ Check whether the large amount of NH3 injection is smaller than the design.

M: Design value for NH3 injection amount (31) The amount of NH3 injection is large. This is because the reaction space temperature is not in the appropriate temperature range when there is a large amount of leaked NH3.

F: Upper limit value of reaction space temperature Arbitrary setting [℃] G: Lower limit value [℃] 0 Leak despite the reaction space temperature being at an appropriate temperature (N)
(The fact that 3 is more common than E indicates the limit of the non-catalytic denitrification method), and the NH3/NOX ratio is too large.

Therefore, the NOx target value is set higher.

As explained above, according to the method of the present invention, it is possible to accurately control the amount of NH3 injection, and the drawbacks of the conventional method such as leakage of Nus and insufficient denitration can be overcome. 1+ This has the effect of preventing failure of the analyzer, etc.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the conventional method, Figure 2 is a conceptual diagram of the method of the present invention,
Figures 3 and 4 are flowcharts, Figure 5 is a graph showing the relationship between reaction space temperature and denitrification rate, and Figures 6 and 7 are N
A graph showing the relationship between Ox concentration and time, and FIG. 8 is a graph showing the relationship between reaction space temperature and leak NH3 concentration. (1)...furnace, (2)--reaction space, (3)...
NH3 source, (4)...control valve, (5)...NOx measuring device, (6)...computing device, (7)...process data. Patent Applicant Nippon Kokan Co., Ltd. Inventor Mitsuki Yamagishi Ryudo Yokoyama Takao Minami Figure 5 → T, μ Tanuki Figure 6 Figure 111 Back Figure 7 Time - m - 8 Zuko μ standing temperature

Claims (1)

[Claims] In the non-catalytic denitrification method, which removes NOx by injecting NHs into high-temperature exhaust gas, the reaction space temperature and the NOx concentration after denitrification are measured, and the amount of exhaust gas after denitrification is calculated or measured, and NOx generation is determined from these values. N'H3 injection into the reaction space (J-0"
[17, L'''' 1111 Method for controlling injection amount of NH in medium 1 method.