JPS6186501A - Method of recovering steam - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a steam recovery method for guiding high-temperature exhaust gas to an exhaust heat boiler to recover heat.

;) Conventional technology The pressure of process steam in steel plants has been lowered year by year due to energy conservation and other efforts. Along with this, the recovery steam pressure of exhaust heat recovery boilers and the like also increases the total amount of recovered heat, so there is a tendency to follow this trend.

However, when the recovery pressure is lowered, the amount of recovered heat increases;
On the other hand, as the exhaust gas temperature decreases, low-temperature corrosion (SO3 and moisture (H2O) in the exhaust gas reacts, causing sulfur @ (
H2SO4) causes corrosion. ), and the recovered steam pressure was set high so that the exhaust gas temperature would be within a safe control temperature for the sulfuric acid dew point. As a result, the temperature difference between the exhaust gas and the heat transfer section of the boiler is small, resulting in a loss of recovered heat.

(c) Problems to be solved by the invention The problems to be solved by the invention are to measure the amount of SO3 in the exhaust gas that affects low-temperature corrosion (sulfuric acid corrosion),
The object of the present invention is to provide a method for obtaining the maximum amount of recovered heat while maintaining the minimum necessary steam pressure.

The steam recovery method of the present invention is a method for recovering heat by guiding high-temperature exhaust gas to a waste heat boiler, in which the exhaust gas temperature (T ) and the amount of SO3 in the exhaust gas, continuously measuring the steam pressure (Pa) in the drum of the waste heat boiler,
Converting the measured SO2 amount to a predetermined sulfuric acid dew point temperature (To), converting the converted temperature (To) and the measured temperature (T
), converting the temperature difference (ΔT) into a predetermined steam set pressure difference (JP) in the drum, and converting the converted pressure difference ( JP) k Add to the above measured pressure (Pa) to create a new set pressure (P=Pa
+ΔP), and by controlling the pressure regulating valve provided on the exit side of the cannon drum based on the set pressure,
The above problems have been resolved.

(E) Embodiment FIG. 1 is a schematic explanatory diagram of equipment for carrying out the steam recovery method of the present invention. In the rotary kiln 1, female plants (for example, railroad ties, scraps, tires, waste paper, etc.), scum, etc. generated in the steelworks are burned.

The heat of the combustion exhaust gas is recovered by an exhaust heat boiler 2 (in this embodiment, a two-fertile water tube boiler), and the soot and dust is collected by an electric precipitator 3, and then sent to a chimney 6 by an induction fan 5 installed in a flue 4.
is discharged.

The high temperature exhaust gas in the boiler 2 exchanges heat with the inside of the boiler heat transfer section 7, and water vapor is generated. Inside the boiler heat transfer section 7, the steam and water are not mixed, and the mixture returns to the boiler drum 8, where only steam is separated from the steam and water.

Steam is sent from the boiler drum 8 to the process steam piping 10 via a pressure regulating valve 9.

A pressure gauge 11 is attached to the boiler drum 8 and sends a steam pressure detection signal to a control device 14. An SO3 detector 12 is attached to the exhaust port of the boiler 2, and SO3
The detection signal is sent to the control device 14. A thermometer 13 is attached to the exhaust port of the electrostatic precipitator 3 and sends an exhaust gas temperature detection signal to a control device 14. The control device 14 sends a control signal to the pressure regulating valve 9.

The control operation of the control device 14 will be explained with reference to FIGS. 1 and 2.

In FIG. 2, as shown in block 141, SO3
The amount of SO3 in the exhaust gas from the detector 12 is converted into a predetermined sulfuric acid dew point temperature (To). T to perform this conversion. The control diagram is shown in Figure 3. This control chart is obtained by plotting the maximum and minimum values of moisture in the exhaust gas on a graph based on past periodic measured values, and using an approximate broken line of the maximum value.

Next, the difference between the actual exhaust gas temperature (T) from the thermometer 13 and the converted sulfuric acid dew point temperature (To) (Δ'r='r0-'r) *
(block 142).

From the temperature difference (ΔT) obtained in this way, the pressure deviation Δ
Find P. As shown in block 143 of FIG. 2 and FIG. 4, the relationship between ΔT and JP determined in advance? Express it in a graph and set the upper and lower limits. The purpose of setting these upper and lower limits is to prevent sudden changes in the set steam pressure within the boiler drum.

Next, as shown in block 144 of FIG. 2, the converted pressure difference (JP) is added to the actual drum pressure (Pa).
P=Pa+ΔP). This pressure Pt'' is set as a new set pressure, but in order to prevent this new set value from exceeding the operating range of the exhaust heat boiler 2, upper and lower limits are also set for the set pressure PS, as shown in block 145. will be established.

The new set pressure (Ps) obtained in this way is compared again with the tram actual pressure (Pa), and the difference (ΔP8-P8
-pa) to control the pressure regulating valve 9.

The upper limit of the boiler operating range mentioned above is the boiler maximum operating pressure, and the lower limit is the boiler maximum steam generation amount. However, in this case, it indicates the volumetric flow rate and represents the capacity of the steam/water separator.

(f) Specific example ■, target exhaust heat boiler specifications (1) Model: 2-fertile water tube type (11) Pressure crab Maximum working pressure = 16atg Normal pressure car 12atg (+ii) Steam temperature: Saturation temperature (1v) Water supply temperature (inside deaerator) = 20°C (■) Evaporation amount 2 5620k
g/hr (vil Exhaust gas temperature 2 Input loaf 43°
'C outlet 2 SO℃ (vlo transmission, reach area: 957m2 (viiD ventilation method: parallel ventilation ■, control result (1) drum pressure before pressure control (recovered steam pressure): 9a
l, g (average value) (11) Tram pressure after pressure control (recovered steam pressure):
6Qatg (average direct) Uii) Boiler outlet exhaust gas temperature decrease: 200℃
(Conventional method 233℃) (1v) Effect 2 3rCX 14400 Nm3/hr
X 0.32 Kcal/Nm3℃-152Xl03
Kcal/hr r152403Kcal/hr X 8
760 hr/YearX O, 75= 998.6
Xl03Kcal/Year According to the method of the present invention, it is possible to sufficiently follow changes in exhaust gas temperature due to differences in fuel, and the minimum recovery steam pressure can be set at a temperature where the exhaust gas temperature is always higher than the sulfuric acid dew point. Therefore, the maximum amount of heat can be recovered while dealing with low-temperature corrosion of the waste heat boiler that recovers heat from exhaust gas containing sulfur.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of equipment for carrying out the steam recovery method of the present invention. Figure 2 is a control block diagram of boiler drum pressure. Figure 3 is a graph showing the relationship between SO3 in exhaust gas and sulfuric acid dew point temperature. FIG. 4 is a graph showing the relationship between temperature deviation and pressure deviation. 1: Rotary kiln 2: Waste heat boiler 3: Electrostatic precipitator 4: Flue 5: Induction fan 6: Chimney 7: Boiler heat transfer section 8: Boiler drum 9: Pressure regulating valve 10: Process steam piping 11: Pressure gauge 12: S○3 detector 1
3: Thermometer 142 Control device patent applicant Sumitomo Metal Industries, Ltd. (5 others)

Claims (1)

[Claims] In a steam recovery method in which heat is recovered by guiding high-temperature exhaust gas to a waste heat boiler, the exhaust gas temperature (T) and the amount of SO_3 in the exhaust gas are continuously measured on the outlet side of the waste heat boiler, The steam pressure in the drum of (P_
a), converting the measured amount of SO_3 into a predetermined sulfuric acid dew point temperature (T_o), and calculating the difference between the converted temperature (T_o) and the measured temperature (T) (ΔT=
T_o-T), converting the temperature difference (ΔT) into a predetermined steam set pressure difference (ΔP) in the drum, and adding the converted pressure difference (ΔP) to the measured pressure (P_a). A steam recovery method comprising: setting the pressure to a new set pressure (P=P_a+ΔP); and controlling a pressure regulating valve provided on the outlet side of the front drum based on the set pressure.