KR20130123025A - Method for operation of a grain drier - Google Patents

Abstract

The present invention relates to a multi-purpose grain drier operating method. In detail, the invention relates to a method for calculating an air flow rate, an air flow temperature, and a circulation speed which are drying factors of a multi-purpose grain drier in order to have high drying efficiency. An operation condition calculating method of the multi-purpose grain drier of the invention includes a step of calculating a water content percentage ratio (MR) of grain according to drying time (t), relative humidity (RH), and temperature of inflow air (T) and a step of calculating drying temperature, an air flow rate, and grain falling speed of the grain drier by using the water content percentage ratio.

Description

Method for operation of a grain drier}

The present invention relates to a method for operating a multi-purpose grain dryer, and more particularly, to a method for calculating a blowing amount, a drying temperature, a circulation speed, which are drying factors of the multipurpose dryer, to have a high drying efficiency.

Grains should be dried to the target moisture in an appropriate way for storage, processing, etc. without changing quality after harvesting.

In general, grains reach a moisture content equilibrium that does not absorb or release moisture after prolonged exposure to air with constant temperature and relative humidity. In this case, the moisture content is referred to as the equilibrium moisture content of a given temperature and relative humidity. High-moisture grains evaporate water from the surface to maintain equilibrium moisture content, and water diffuses simultaneously to the surface. This phenomenon is called drying process.

At this time, if the diffusion rate is slower than the drying rate, the water content difference occurs inside and outside the grain and the stress increases. That is, as the drying proceeds, a large difference in stress is generated, and a copper charge, which is a cause of deterioration of grain, is generated. Tempering is to stop drying for a certain time and to leave grains to reduce the difference in moisture content between the grains inside and outside the grains. During the tempering, the difference in moisture content during drying is due to the diffusion of moisture inside the rice grains to the surface. Since is reduced, the occurrence of copper activity is suppressed.

In general, water evaporation of grains requires more energy than evaporation of free water, and latent heat of evaporation is required for surface evaporation. Water evaporated from the surface is removed by convection or blowing air. If the internal moisture diffusion rate is greater than the water removal rate due to surface evaporation, the constant drying rate is constant. On the contrary, if the internal diffusion rate is less than the surface evaporation rate, the drying rate decreases.

As shown in FIG. 1, the basic form of grain drying is a concurrent flow type in which the flow of grain and hot air is in the same direction, a counter flow type in the opposite direction, as shown in FIG. Orthogonal cross flow type, mixed flow and mixed grains are divided into fixed-bed type where static and hot air only move.

Grain dryers used in Korea include hot air drying type circulating dryers and continuous dryers, normal temperature ventilation drying type silos, square bins, etc. In general, circulating dryers are cross flow type, continuous dryers are mixed flow type and Room temperature ventilation drying is a fixed bed type. The hot air drying type circulating dryer and the continuous dryer are configured to repeat drying → tempering → drying → tempering process in order to minimize the occurrence of frost. The circulating dryer uses the upper storage part inside the dryer for tempering. Since the continuous dryer does not have a tempering area inside the dryer, a separate tempering bin is required, and the room temperature ventilation drying does not require a tempering process because the drying speed is low.

The conventional cross-flow type circulating dryer, which is most commonly used in Korea, is limited to single grain species (rice, barley) due to the blockage of the perforated network depending on the grain size.

The multi-purpose dryer has a structure without perforation inside to allow multi-purpose drying of rapeseed seeds including barley, barley, corn and soybeans, and adopts a co-current type, that is, a hot air stream and a grain flow have the same co-flow. All grains are exposed to the same hot air, initially exposed to high temperatures but discharged to low temperatures. Therefore, the multi-purpose drier is a drier which can suppress the generation of copper and save energy while ultrafast drying with high temperature hot air (100-120 ° C.).

The grain-circulating cocurrent grain dryer is registered with a patent. The patent name is 'RICE CIRCULATING CONCURRENT-FLOW DRYER, 10-0968966.' However, the circulating cocurrent grain dryer patent relates to a dryer device and structure, and does not disclose a method of operating the dryer, types of dry grains and drying conditions (air flow rate, blowing temperature, grain circulation rate). In general, the important factors that affect the performance of grain dryers are the blowing amount, blowing temperature, and circulation speed, and these factors affect the drying speed, quality of dry grain, and drying energy.

The problem to be solved by the present invention is to propose a method for calculating the blowing amount, the blowing temperature, the circulation speed of the dryer having the optimum drying conditions.

Another problem to be solved by the present invention is to propose a method for calculating the blowing amount, blowing temperature, circulation speed of the dryer having the optimal drying conditions according to the type of grain.

Another problem to be solved by the present invention is to propose a method for calculating the optimum drying conditions by applying different equations according to the type of grain.

To this end, the method for calculating operating conditions of the multipurpose grain dryer of the present invention includes calculating a moisture content ratio (MR) of grains according to a drying time (t), a relative humidity (RH), and an air temperature (T) introduced therein. Calculating a drying temperature, a blowing amount, and a grain fall rate of the grain dryer using the moisture content ratio.

The multi-purpose grain dryer according to the present invention is to analyze the drying process by a mathematical method to minimize the change in quality when drying rice, rapeseed seeds, barley, corn, soybeans in the multi-purpose grain dryer at the same time minimum drying energy, maximum drying There is an advantage to having speed. That is, by applying a suitable equation according to the properties of the grain it is possible to implement a multi-purpose grain dryer with efficient drying.

1 shows various drying methods of a grain dryer,
2 shows a multipurpose dryer according to the invention,
3 illustrates a stationary drying model according to an embodiment of the present invention,
4 shows a parallel model,
Figure 5 shows the drying characteristics of the rapeseed seeds according to the change in the blowing amount,
Figure 6 shows the drying characteristics of the rapeseed seed according to the change in flow rate,
7 shows the drying characteristics of the rapeseed seed according to the change of hot air temperature,
8 shows the drying characteristics of the barley according to the change of air volume,
Figure 9 shows the drying characteristics of the barley according to the change in flow rate,
10 illustrates the drying characteristics of barley according to the change in hot air temperature.

The foregoing and further aspects of the present invention will become more apparent through the preferred embodiments described with reference to the accompanying drawings. Hereinafter will be described in detail to enable those skilled in the art to easily understand and reproduce through this embodiment of the present invention.

2 shows a multipurpose dryer according to the invention. As shown in FIG. 2, the dry air absorbs moisture from the grains while passing through the grain layer, whereby the humidity increases and the temperature decreases, while the grains lose moisture and the grain temperature rises. As such, the target moisture content is reached while repeating the drying-circulation-tempering process.

The drying model representing the drying rate of the grain can be classified into a thin layer drying model and a thick layer drying model. The thin layer drying model represents a drying process of a thin layer of grain, and the thick layer drying model represents a drying process consisting of a plurality of thin layers. In other words, the moisture content (M), grain temperature (θ), air temperature (T) and absolute humidity (H) of the grain are functions of the location and time of the grain layer. Equations that describe changes in moisture content, grain temperature, air temperature and absolute humidity in the rear layers are called deep bed drying models.

3 illustrates a stationary drying model according to an embodiment of the present invention. Hereinafter, a fixed dry model according to an embodiment of the present invention will be described with reference to FIG. 3.

The required equation can be derived by taking into account the moisture and energy equilibrium for the grains in the microvolume AΔx and the dry air passing through them at any depth x of the fixed grain layer. Unknown variables are the moisture content and grain temperature of the grain, the temperature and absolute humidity of the air passing through the grain bed.

        M (x, t) = grain moisture content (dec., D.b.)

        θ (x, t) = curved temperature (℃)

        H (x, t) = absolute humidity of air (kg-water / kg-dry air)

T (x, t) = dry bulb temperature of air (℃)

Hereinafter, four differential equations including four unknown variables will be derived based on mass and energy balance.

(1) Water equilibrium for grains in microvolumes

The following symbols are defined to account for the water balance for grains in the microvolume AΔx.

= 곡물 단위체적당 단위시간당 곡물의 수분증발율(kg/hr.m³)

= Moisture evaporation rate of grain per unit time per grain volume (kg / hr.m ³ )

A = cross-sectional area of the grain layer (m ² )

ε = porosity of grain layer (dec.)

ρ = true density of dried grain (kg / m ³ )

  About grain in microvolume,

 Water inflow rate = 0

Substituting in the mass balance equation,

 If we apply the mean theorem,

  Equation 2 is an equation representing the drying rate that can be obtained by differentiating the thin layer dry equation of the grain. It is expressed as a function of the moisture content (M) of the grain, the temperature (θ) of the grain, the temperature (T) of the hot air and the absolute humidity (H) of the dry air. In other words,

(2) Water balance in air in microvolumes

The following symbols are defined to take account of the water balance in the air within the microvolume AΔx.

= 단면적당 건공기 질량유량(kg/hr.m²)

= Dry air mass flow rate per cross section (kg / hr.m ² )

= 건공기 밀도(kg-dry air/m³)

= Dry air density (kg-dry air / m ³ )

= 건조곡물의 산물밀도(kg/m³)

= Product density of dried grains (kg / m ³ )

The control volume becomes a void in the micrograin layer, and considering the water vapor equilibrium,

Substituting in the mass balance equation,

If we apply the mean theorem,

The right side term, which represents the rate of change of moisture in the air in the void, has a very small value, as at home,

(3) Energy balance for air in microvolumes

The following terms are defined to consider the energy balance for air in microvolumes.

= 수증기 엔탈피(kJ/kg)

= Water vapor enthalpy (kJ / kg)

= 건공기 엔탈피(kJ/kg)

= Dry air enthalpy (kJ / kg)

= 곡물층의 대류열전달계수(kJ/hr.m².℃)

= Convective heat transfer coefficient of grain layer (kJ / hr.m ^2. ℃)

a = specific surface area of the grain layer (= grain surface area per unit volume of grain layer, m ² / m ³ )

If we apply the mean value theorem to the energy balance equation,

Differentiate and expand,

To multiply Equation 5 by,

If Equation 8-Equation 9 is calculated,

Specific heat is defined as

Specific heat of dry air

Specific heat of water vapor

therefore,

Substituting the above into the equation (10),

The right side term representing the rate of change of air energy in the void of Equation 11 may be omitted since it is a very small value as in the home.

(4) Energy equilibrium for grains in microvolumes

= 곡물내의 수분엔탈피(kJ/kg)

= Water enthalpy in grains (kJ / kg)

= 건조곡물 엔탈피(kJ/kg)

= Dry grain enthalpy (kJ / kg)

If we apply the mean value theorem to the energy balance equation,

Specific heat is defined as

Specific heat of dry grains:

Specific heat of moisture in grains:

therefore

  Substituting this in Equation 13,

는 곡립에서 증발된 수분(수증기)의 엔탈피와 곡립내의 수분(물)의 엔탈피의 차이다. 이는 곡립내의 수분을 증발시키는데 필요한 에너지와 증발된 수분을 공기의 온도까지 상승시키는데 요구되는 에너지의 합이다. 즉,here,

Is the difference between the enthalpy of water (vapor) evaporated from the grain and the enthalpy of water (water) in the grain. This is the sum of the energy needed to evaporate the moisture in the grain and the energy required to raise the evaporated water to the temperature of the air. In other words,

는 곡립내의 수분증발잠열이다.
here,

Is latent heat of evaporation in the grain.

Substituting Equation 15 into Equation 14,

Summarizing Equation 3, Equation 6, Equation 12, and Equation 16 derived above,

수학식 3

Equation 3

수학식 6

Equation 6

수학식 12

Equation 12

Equation 16

The four differential equations constitute the mathematical model of the fixed bed drying process. The solution of this differential equation (the strict solution) is not available, and the numerical solution is used to approximate the solution. The boundary and initial conditions are as follows.

: 곡물의 초기온도

: Initial temperature of grain

: 유입공기의 온도

: Temperature of inlet air

: 유입공기의 절대습도

: Absolute humidity of inlet air

Hereinafter, the thick layer drying model will be described in detail.

4 shows a conceptual diagram of an equilibrium model. Hereinafter, the conceptual diagram of the equilibrium model will be described in detail with reference to FIG. 4.

시간 건조 후에 곡물에서

의 수분이 증발하여 배출공기에 첨가되므로 곡물의 함수율은

만큼 감소된

가 되며, 배출공기의 습도는

만큼 증가하여

가 된다. 또한 곡온은

만큼 상승하여

가 되며 배출공기의 온도는 곡온상승 및 수분증발에 의한 냉각효과에 기인하여

만큼 하강하여

가 된다. I층에서 배출된 온도

와 절대습도

의 공기는 I+1층의 유입공기가 된다. 이러한 과정을 전체 박층에 걸쳐서 연속적으로 계산하면 후층건조를 해석할 수 있다.
4 shows the change that occurs in the Ith thin layer by dividing the thick layer into N thin layers. If the temperature of the air entering the I layer is T _o , the absolute humidity is H _o , the grain moisture content is M _o , and the grain temperature is G _{o ,}

In grain after drying time

Moisture is evaporated and added to the discharged air,

Reduced by

And the humidity of the exhaust air

Increased by

. In addition, the grain temperature

Up by

The temperature of the exhaust air is due to the cooling effect due to the rise of grain temperature and moisture evaporation.

Down by

. Temperature emitted from layer I

And absolute humidity

Air becomes the inlet air of the I + 1 layer. Continuous calculation of this process over the entire thin layer can be used to analyze thick layer drying.

In addition, the thin drying model of each grain and rape seed is as follows.

rice plant

barley

Rape seed

bean

corn

MR: moisture content ratio

RH: relative humidity

T: temperature of the introduced air

Using the above equations, input the specifications of the dryer, the condition of the grain to be dried, the condition of the outside air, and the condition of the dry air to circulate the number of cycles, tempering time, dry air exposure time, dry moisture content, drying rate, grain temperature, perfect taste. Yield and required energy are calculated. The specifications of the dryer are the main specifications of the drying chamber, and the conditions of the grain to be dried are the initial input weight, the initial water content, the final water content and the flow rate.The conditions of the outside air are the outside temperature and relative humidity, and the conditions of the dry air are the drying temperature. And the blowing amount.

In order to verify the model by the mathematical formula, the drying temperature was 110 ℃, the initial grain temperature was 20.0 ℃, the average outside air temperature was 25.4 ℃, the outside air humidity was 71.6%, the circulation rate was 4.5m / h, and the air flow was 8.1cmm. Drying experiments were conducted under the conditions of / ㎥ and the drying time, final moisture content, drying rate, germination rate, and required energy were measured. The results are compared with those of the mathematical model.

division Experimental results Results by Mathematical Model Drying time (h) 4.25 4.25 Final function rate (%, d.b.) 11.4 10.8 Drying rate (%, d.b./h) 2.80 2.95 Germination rate (%) 94.7 96.5 Required Energy (kJ / kg-water) 4831 4417

Optimum conditions (high drying rate) under various drying conditions (airflow blowing temperature and grain circulation rate) to determine drying conditions that maximize drying speed, minimize required energy, and minimize quality change when drying rice, rapeseed seeds, barley, corn and soybeans. Speed, good quality, small required energy). Figure 5 shows the drying characteristics of rapeseed seeds according to the change of air flow rate, Figure 6 shows the drying characteristics of rapeseed seeds according to the change of flow rate, Figure 7 shows the drying characteristics of rapeseed seeds according to the change of hot air temperature It is shown.

In addition, Figure 8 shows the drying characteristics of the barley according to the change of air flow rate, Figure 9 shows the drying characteristics of the barley according to the change of flow rate, Figure 10 shows the drying characteristics of the barley according to the change of hot air temperature It is shown.

Table 2 below shows the optimal operating conditions to mathematically analyze the drying process of the multipurpose grain dryer to minimize the quality change, minimize the energy required for drying, and maximize the drying speed when drying rice, rapeseed seeds, barley and corn in the multipurpose grain dryer. have.

rice plant Rape seed barley corn bean Drying temperature
(℃) 110 110 110 120 105 Air flow
(cmm / ㎡) 35.0 30.0 26.0 25.0 25.0 Grain Flow Rate
(m / h) 3.0 5.5 5.5 3.5 5.0

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention .

Claims (9)

Calculating the moisture content ratio (MR) of the grains according to the drying time (t), the relative humidity (RH), and the temperature (T) of the introduced air;
And calculating a drying temperature, an air blowing amount, and a grain dropping speed of the grain dryer using the calculated moisture content ratio.
The method according to claim 1, wherein the water content ratio is calculated by the following equation when the grain is rice.

The method of claim 1, wherein when the grain is barley, the moisture content ratio is calculated by the following equation.

The method of claim 1, wherein the water content ratio is calculated by the following equation when the grain is a rapeseed seed.

The method of claim 1, wherein the moisture content ratio is calculated by the following equation when the grain is soybean.

The method of claim 1, wherein the water content ratio is calculated by the following equation when the grain is corn.

The method according to any one of claims 2 to 6, wherein the hot air temperature of the dryer with respect to the depth of the grain layer is calculated by the following equation.

The method of claim 7, wherein the temperature of the grain with respect to the drying time is calculated by the following equation.

10. The method of claim 8, wherein the moisture of the grain with respect to the depth of the grain layer is calculated by the following equation.

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