JPS60228690A - Controlling method of steel plate drying apparatus - Google Patents

Abstract

PURPOSE:To dry a steel plate with necessary quantity of heat of min. limit and to economize energy consumption by controlling the proportion of recirculating air in accordance with various kinds of outer conditions in the titled apparatus of recirculation type. CONSTITUTION:Sucking air 31 is sucked with a blower 1 via a damper 11 and heated with a heat exchanger 2 and sent into a gas jet chamber 3 incorporated in a dryer main body 5. Hot air is blown on the steel plates 20 conveyed continuously from the nozzles 4 of the chamber 3 to evaporated the moisture on the surface of the steel plates and the exhaust gas 32 high in humidity is discharged via a camper 12. A damper 13 is provided on the way of a recirculating air pipe 33 communicating the upstream of the damer 12 and the downstream of the damper 11 to recirculate one part of the exhaust gas. Therein, the ideal coefficient of recirculation is calculated by measuring each quantity and flow rate of the sucked air, the air of a dryer outlet and the blown-out air, the quantity and concn. of vapor contained in each air of these and each temp. of the steel plates at a dryer inlet and the blown-out air. The dampers 11-13 are regulated so that the difference between the calculated coefficient and the real coefficient of recirculation becomes within the preset allowable value.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to the control of a drying device (dryer) that removes water adhering to a thin steel plate and dries the thin steel plate after washing the thin steel plate with water. Regarding the method.

(1) [Prior Art and Problems] FIG. 1 is an explanatory diagram of a conventional dryer for forcibly drying a thin steel plate. Such dryers are used because large quantities of steel sheets must be quickly washed and dried.

In FIG. 1, intake air 31 is taken in by a blower 1, heated by a heat exchanger 2, and then heated by a gas chef 1.
- A thin steel plate (hereinafter referred to as "steel plate") 2 that enters the chamber 3 and moves in the longitudinal direction with water attached to it through the nozzle 4
sprayed on o. This blown air hits the steel plate at 1
The remaining water is evaporated and contained as water vapor, which is exhausted as highly humid air 32.

However, in the open type shown in FIG. 1, the hot air blown onto the steel plate 2o is dispersed straight away, and therefore it is not possible to absorb moisture up to the absolute humidity possible for the temperature of the hot air. This means that the capacity and energy of the blower 1 and heat exchanger 2 are wasted.

In order to improve this point, as shown in FIG. A part of the exhausted exhaust gas 32 is guided to the intake port of the blower 1 as recirculated air 33 to reuse the hot air, and after absorbing sufficient water vapor, the air is discharged.

However, even with the equipment shown in Figure 2, the equipment was conventionally operated in a fixed manner to ensure that the steel plates being carried out were sufficiently dried regardless of conditions such as outside air temperature, humidity, and steel plate temperature. Therefore, extra energy is input to operate the blower 1 and the heat exchanger 2, resulting in a lot of waste.

[Object of the Invention] Therefore, the object of the present invention is to provide a recirculation type dryer as shown in FIG. 2, which blows air by controlling the proportion of recirculated air according to various external conditions. The goal is to save energy by adjusting the amount of heat applied to the air and drying the steel plate with the minimum necessary amount of heat.

[Configuration of the Invention] (3) In order to achieve this object, the present invention provides a control method for a steel plate dryer that recirculates a portion of exhaust gas, in which the intake air mass flow rate (Gga) and the water vapor mass concentration in the intake air are controlled. (
Wa), air mass flow rate at the dryer outlet (GgI), water vapor mass concentration in the air at the dryer outlet (INy), temperature of the steel plate at the dryer inlet (TsI), blown air mass flow lft (Ggt), blown air temperature (
Tgx) and water vapor mass concentration in the blown air (W+
), calculate the ideal recirculation rate (X), and calculate the ideal recirculation rate (X) and the actual recirculation rate ((Ggr-Gga) /G
It is characterized in that the damper that controls the air flow rate is adjusted so that the difference from g1IIl is within a set tolerance value (ε).

Calculation 111 of the value of (X) is based on the following equation.

Gu -Wa GgIII10WImax (Ggp-G
w ) GW = cgφ-GgI WImax is ΔT-(Q N) / (t ・r ・Cp5 ・dx
) (4) Q-α(Tgx -Tsx) dx Ls ・60 M-α. ρ (Ws − Wgx) x dx・3600 I, S・60 60・Ls Gu=(ΣM)・□ This is the maximum value of Wl from dx.

[Embodiments of the invention] The present invention will be explained in detail below with reference to the illustrated embodiments.

The main equipment of the steel plate dryer is shown in Figure 2. The intake air 31 is sucked in by the blower 1 via the intake air damper 11, heated by the heat exchanger 2, and sent to the gas jet chamber 3 in the dryer body 5. Hot air is blown from the nozzle 4 of the chamber 3 onto the continuously conveyed steel plate 20 to evaporate water on the surface of the steel plate,
The humid exhaust gas 32 is discharged through the exhaust damper 12. Further, a recirculation air pipe 3 (5) 3 is provided which communicates the upstream side of the exhaust damper 12 and the downstream side of the intake air damper 11, and a recirculation air damper 13 is provided in the middle of the pipe, and a part of the exhaust air is recirculated. let

(a) The method for controlling the steel plate dryer according to the present invention includes the mass flow rate Ggl of air blown onto the steel plate 20 and its temperature T.
When determining gI, nozzle dimensions, and dryer dimensions, calculate the maximum amount of water vapor possible to dry the water adhering to the steel plate 20, further calculate the amount of recirculated air at that time, and determine the operating conditions. It is something.

(b) The calculation method for exhaust gas temperature and water evaporation amount is as follows.

The steel plate 20 is divided into minute division sections dx (n>) (third
), the steel plate temperature drop ΔT is determined by the following balance equation.
Calculate C"C,) and the amount of water evaporation.

ΔT-(Q-N)/(t・γ・Cps-d)(℃)
...(1) However, the amount of heat transfer ΔQ from the blown air to the steel plate for dx/Ls (n+in) time is (6) (Kcal) ・ ・ ・ ・ (2) N=L −M (Kcal) ・ ・ ・+3) Specific weight of γ Ni strip (thin steel plate) (kg/a) Cps Specific heat of Ni strip (Kcal/kg ・”c) α:
Heat transfer coefficient of hot air (Kcal/n?l+r”c)T
gx: Warm air temperature (°C) Tsx: Local strip temperature ("C) (Numerically integrate equation (1) up to the relevant point and subtract from Tst) Ls Niline speed (m/m1n) ■, : Latent heat of vaporization at that steel plate temperature (Kcal/k
g) t: Half the thickness of the steel plate (m).

Also, the amount of water evaporation M between dx/Ls (min) is
M - αo × ρ
s: Saturated water vapor mass concentration at Ts Wg1: Water vapor mass concentration of hot air.

In addition, water vapor mass concentration W 18.01 ・　・　・(5) however, Δp: Water vapor partial pressure (mmAq) It is.

Further, the temperature Tsp of the steel plate when the steel plate passes through the dryer outlet is Tsf - TsI - ΣΔT (''c) (6 squares, where ΣΔT is the sum of the temperature drops of the steel plate in each minute section.

(8) Also, the amount of water evaporation Gw in the dryer is x It is.

In addition, the exhaust temperature Tst is: ・ ・ ・(8) However, G: Mass flow rate (kg/min) Cp: Specific heat (Kcal/kg'c) T: Temperature (
'C), where the subscript g is air, S is steel plate, W is water, 1 is inlet,
φ represents the exit.

The maximum amount of water vapor in the air that can be used to evaporate the water adhering to the steel plate 20 is determined by repeatedly calculating the amount of water vapor in the air from the above-mentioned equations +11 to (8), and this value is set as WIIIlax.

(c) Next, find the ratio X(9) of the recirculation amount to the dryer outlet mass flow rate so that Wlmax determined in the previous section is achieved.

Since the mass must be the same before and after the change, Gg1-xGg16+Gga...(9)Gg16
GgI =c-... ・-aO)WImaxGgx
-W a Gga -x (Gw +Vl/jn+axGgI)...(1
1) From the 00) formula, Ggl = Gg91-0 weak (9), from the 001 formula, Gga = Ggpl - Gw -x, Gg5d Substitute this into the formula (11), Wl max (Ggl-Gw ) = Wa (Ggy3-Gw-x Gg9)=x (G
w +Wzmax (Gg/8-0%4) 1 deformation, x (Gw -Wa Ggφ+W1max (Ggp-
Gw ) 1=WImax (Ggy3-Gw ) −
Wa (Gg5+l-Gw) From now on, (10) (Wlmax-Wa) (Ggl-Gu)Gw -
Wa GgP+Wrmax (Gglr-Gw)・
・ ・ (12) becomes. However, Wa is the water vapor mass concentration in the intake air.

This is the operating condition, and the value of the recirculation amount ratio X is expressed by the formula (1
2), the intake air damper 11,
The opening degrees of the exhaust damper 12 and the circulating air damper 13 are adjusted.

(d) The heating amount QH of the heat exchanger 2 under this operating condition is QH-(xGgφ+Gga) CpgITg, t-x
(Ggll!ICpg5IITg#)-GgaCpga
Tga can be determined by (13).

(e) Now, measure the following quantities required to execute the control.

・Water vapor mass concentration (Wa) in the intake air ・Blowout air temperature (Tgl) The heating amount of the heat exchanger 2 is controlled by this.

(11) ・Water vapor mass concentration in the blown air (Wl) ・Water vapor quality in the dryer outlet air Wtt11 degrees (Wt) ・Dryer outlet air mass flow N CGgp) ・H4 plate temperature at the dryer inlet (TsL) ・Blowed air mass Flow rate (G
gI) - Intake air mass flow rate (Gga) Ggl, Ggp) measured in completely dry conditions.

From the values of Wt and Wt, the amount of water adhering to the steel plate 20, that is, the amount of water evaporation Gw is determined by the following formula: Gw=WφGgp−WI Gg1.

Using this value of Gw, fl~
Execute the sequential calculation of equation (8), calculate W1maχ, and (
12) Subtract X from the formula. Then, the intake air damper 11. The opening degrees of the exhaust damper 12 and the circulating air damper 13 are controlled.

(f) FIG. 4 is a flowchart of this control method.

(ε) in the figure indicates that this control system is overly activated (12). This is an appropriately set tolerance value that does not change.

(I.) As explained above, the steel plate dryer control method according to the present invention uses known sensors to determine the intake air water vapor concentration (Wa), the inlet water vapor concentration (Wz), the outlet water vapor concentration (Wθ), and the intake air flow rate. (Gga), inlet flow 1
M (GgI), outlet flow rate (Ggp).

By measuring the inlet temperature (Tgz) and steel plate temperature (Tsl) and inputting them into the computer,
The optimum conditions are calculated, and the heating amount of the heat exchanger 2 is adjusted and the dampers 11, 12, . and 13 to set the recirculation ratio by controlling the opening degree.

That is, if the recirculation ratio (X) is increased from this operating condition, the water adhering to the steel plate 20 cannot be completely removed and dried. Further, when (X) is decreased, the amount of heating (QH) of the heat exchanger 2 increases, resulting in energy loss.

(H) FIG. 5 shows an example of calculation of operating conditions and the heating amount reduction ratio with respect to the conventional method.

The data for each point in the figure is as follows.

(13) [Effects of the Invention] As explained in detail above, according to the present invention, in the drying method using a recirculating steel plate dryer, the hot air blown onto the steel plate to remove moisture adhering to the steel plate has Since the Hyouka Kiun 1III capacity can be controlled to 100% utilization, the steel plate can be completely dried and the amount of heating (14) in the heat exchanger can be minimized, so the energy required for drying can be minimized. can do.

[Brief explanation of drawings]

Fig. 1 is a system diagram of an open type steel plate dryer, Fig. 2 is a system diagram of a recirculation type steel plate dryer, Fig. 3 is an explanatory diagram of minute parts of a steel plate, and Fig. 4 is a system diagram of a steel plate dryer according to the present invention. The flowchart of the control method, FIG. 5, is a graph showing the recirculation flow rate and heating amount ratio. In the figure, 1 is a blower, 2 is a heat exchanger, 3 is a gas jet chamber, 4 is a nozzle, 5 is a dryer main body, 11
12 is an intake air damper, 12 is an exhaust damper, 13 is a circulating air damper, 20 is a steel plate, 31 is an intake air, 32 is an exhaust, 3
3 is a circulating air pipe. Applicant Mitsubishi Heavy Industries, Ltd. Sub-Agent Patent Attorney Hara 1) Yukio (15) Figure 1 Figure 2! :14

Claims (1)

[Claims] In a method of controlling a steel plate drying apparatus that allows part of the exhaust gas to be circulated, an intake air mass flow rate, a water vapor mass concentration in the intake air, a dryer outlet air mass flow rate, a water vapor mass concentration in the dryer outlet air, Steel plate temperature and blown air mass flow rate at the dryer inlet. The temperature of the blown air and the mass concentration of water vapor in the blown air are measured, the ideal recirculation rate is calculated, and the air flow rate is controlled so that the difference between the ideal recirculation rate and the actual recirculation rate is within a set allowable value. A method for controlling a steel plate drying device, the method comprising: adjusting a damper for controlling a steel plate drying device.