Temperature control method for large precooling concrete mixing plants

Abstract

The present invention relates to a temperature control method suitable for a large-scale precooling concrete mixing plant, and the steps are: measuring the ambient temperature at the location of the mixing plant; measuring the surface temperature of coarse aggregate and fine aggregate when they are stored in a storage shed and the temperature of cementitious materials in a storage tank; measuring the surface temperature of coarse aggregate, fine aggregate and cementitious materials when they are transported to the mixing plant and before they are put into use; establishing a calculation model for the relationship between the temperature change value of coarse aggregate, fine aggregate and cementitious materials from storage to before they are put into use and the ambient temperature, and obtaining the temperature characteristic parameters of coarse aggregate, fine aggregate and cementitious materials as the ambient temperature changes; determining the speed of the conveyor conveying coarse aggregate, the air outlet temperature of the air cooler, the cold water temperature and the amount of flake ice used under different ambient temperatures. The present invention can optimize the air outlet temperature, cold water temperature and the amount of flake ice used of the precooling equipment of the mixing plant production system under the premise of meeting the precooling concrete outlet temperature requirement (16°C), so as to achieve optimal resource allocation.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete mixing, and in particular relates to a temperature control method suitable for a large precooling concrete mixing plant. Background Art

[0002] Because the heat generated by the internal hydration temperature rise of large-volume concrete after pouring cannot be dissipated into the air in time, the temperature inside the concrete structure first rises and then drops. Accordingly, the concrete first exhibits compressive stress and then tensile stress. Once the tensile stress inside the concrete exceeds the tensile strength of the concrete, the large-volume concrete will crack.

[0003] An important factor affecting the tensile stress amplitude of concrete is the production temperature of concrete, that is, the outlet temperature of the concrete mixing plant, that is, the temperature of the concrete ready for pouring generated by the concrete mixing plant after mixing various raw materials. The lower this temperature is, the lower the maximum temperature of the concrete hydration reaction is, the lower the temperature drop from the maximum temperature to the ambient temperature is, the smaller the final tensile stress inside the concrete is, and the smaller the risk of cracking is.

[0004] At present, in large-volume concrete projects, in order to effectively control concrete cracks, the concrete outlet temperature is generally controlled at high temperatures in summer, usually between 7°C and 14°C, depending on the importance of the building's location and the different structural forms.

[0005] However, in the southern regions (such as Hubei, Hunan, Jiangxi, etc.) in the hot summer, the natural temperature of concrete at the outlet is generally around 30℃. To reduce it to 7℃ or 14℃, it is not enough to rely on a single pre-cooling measure. The commonly used measures are: 1) Pre-cooling concrete with the "three-cooling method": first, water-cool the aggregate, usually soaking the aggregate in a tank with 2-4℃ cold water, or using the spray method to water-cool the aggregate on a special water-cooled aggregate conveyor belt machine to cool the aggregate to about 10℃, then air-cool the aggregate in the mixing plant silo, and finally mix the concrete with flake ice instead of water. The comprehensive measures of the "three-cooling method" can reduce the temperature of the concrete outlet to 7℃. This technology is suitable for projects with no secondary screening of the aggregate system and open construction sites. 2) "Twice air-cooled aggregate and ice-adding" technology to pre-cool concrete. The twice air-cooled aggregate technology is to use cold air to cool the coarse aggregate in the ground aggregate bin for the first time, and then transfer the aggregate to the mixing plant bin for the second time. The aggregate is cooled to about 8℃ for the first time, and the final temperature of the aggregate is cooled to about 0℃ for the second time. Finally, flake ice is used instead of water to mix the concrete. The comprehensive measures of "twice air-cooled aggregate and ice-adding" can stably reduce the temperature of the concrete outlet to 7℃ or even lower.

[0006] In addition, for major national projects, the outlet temperature of concrete will also be controlled at 12-14℃. The cooling combination methods at this time are mainly 1) using cold air in the mixing plant silo to cool aggregates, and then using flake ice instead of water to mix concrete; 2) using the ground aggregate silo for one-time air cooling and the mixing plant silo for two-time air cooling to operate in combination; 3) using the ground aggregate silo for one-time air cooling and adding flake ice to mix concrete in combination.

[0007] With the development of green and low-carbon construction technology in my country, studies have shown that in an environment with short transportation distances and low temperature growth after concrete production, adjusting the concrete outlet temperature to 16°C can effectively improve concrete production efficiency, while reducing the use of secondary air cooling, cold water, and flake ice, achieving the goal of green and low-carbon construction.

[0008] In this project, the concrete is required to be cooled by air, iced, and cold water once to achieve the requirement that the outlet temperature of the pre-cooled concrete reaches 16°C. Therefore, after 5 months of data monitoring, this patent obtains the characteristic parameters of coarse aggregate, fine aggregate, and cementitious materials changing with ambient temperature through a large amount of data fitting, and further obtains the relationship function between the coarse aggregate cooling time (the conveying time of the belt conveyor that transports coarse aggregate), the outlet temperature of the air cooler, the cold water temperature, the amount of flake ice used, and the concrete outlet temperature of 16°C. The outlet temperature of the pre-cooled concrete can be accurately controlled at around 16°C, and the optimal solution for the resource allocation of the mixing plant can be achieved by reasonably adjusting the coarse aggregate air cooling time, the outlet temperature of the air cooler, the temperature of the cold water added, and the amount of flake ice used, saving resources and costs, and achieving the goal of green and low-carbon production of concrete. Summary of the invention

[0009] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a temperature control method suitable for a large pre-cooling concrete mixing plant.

[0010] The present invention solves the technical problem by the following technical solutions:

[0011] A temperature control method applicable to a large pre-cooling concrete mixing plant, characterized in that the temperature control method comprises the following steps:

[0012] Step 1) Determine the ambient temperature at the mixing plant location;

[0013] Step 2) Determine the surface temperature of coarse aggregate and fine aggregate when stored in the storage shed and the temperature of cementitious material in the storage tank;

[0014] Step 3) Determine the surface temperature of coarse aggregate, fine aggregate and cementitious materials in the storage shed and storage tank before they are transported to the mixing plant and put into use;

[0015] Step 4) By collecting a large amount of data from steps 1) to 3), a relationship model between the temperature change values ​​of coarse aggregate, fine aggregate and cementitious material from storage to before being put into use and the ambient temperature is established, and characteristic parameters of coarse aggregate, fine aggregate and cementitious material changing with the ambient temperature are obtained by fitting;

[0016] Step 5) According to the relationship model between the amount of coarse aggregate, the transportation speed of coarse aggregate, the air outlet temperature of the air cooler, the cooling temperature of coarse aggregate and the characteristic parameters of coarse aggregate changing with the ambient temperature obtained in step 4), the conveying time of the belt conveyor for transporting coarse aggregate and the air outlet temperature of the air cooler are obtained;

[0017] Step 6) obtaining the cold water temperature according to the relationship model between the fine aggregate dosage, the fine aggregate cooling temperature, the cold water temperature, the cold water dosage, the cooling temperature of the fine aggregate and cold water mixture and the characteristic parameter of the fine aggregate changing with the ambient temperature;

[0018] Step 7) determining the amount of flake ice to be used according to the relationship model between the amount of cementitious material used, the target value of concrete cooling temperature and the characteristic parameter of the cementitious material changing with the ambient temperature;

[0019] Step 8) Optimize the cycle from step 4) to step 7) to determine the air outlet temperature of the air cooler, the cold water temperature and the amount of flake ice used under different ambient temperatures.

[0020] Moreover, the specific process of step 4) is as follows:

[0021] By collecting a large amount of measured data, the temperature change value △T of coarse aggregate from storage to before it is put into use is established. c1 The relationship model with the ambient temperature T0 can be fitted to obtain the characteristic parameter n1 of coarse aggregate changing with ambient temperature:

[0022] △T c1 =|T c1 -T c0 |=|T c0 -T0|*[e^(-n1t)-1] (1)

[0023] in,

[0024] △T c1 It is the temperature change value of coarse aggregate from storage to before it is put into use;

[0025] T c1 The surface temperature of the coarse aggregate transported to the mixing plant before being put into use;

[0026] T c0 It is the surface temperature of coarse aggregate when it is stored in the storage shed;

[0027] T0 is the ambient temperature at the mixing plant location;

[0028] t is the time factor, which is normalized and taken as 1 in calculation;

[0029] n1 is the characteristic parameter of coarse aggregate that changes with ambient temperature;

[0030] By collecting a large amount of measured data, the temperature change value △T of fine aggregate from storage to before it is put into use is established. x1 The relationship model with the ambient temperature T0 is fitted to obtain the characteristic parameter n2 of fine aggregate changing with ambient temperature:

[0031] △T x1 =|T x1 -T x0 |=|T x0 -T0|*[e^(-n2t)-1] (2)

[0032] in,

[0033] △T x1 It is the temperature change value of fine aggregate from storage to before it is put into use;

[0034] T x1 The surface temperature of fine aggregate transported to the mixing plant before being put into use;

[0035] T x0 It is the surface temperature of fine aggregate when it is stored in the storage shed;

[0036] n2 is the characteristic parameter of fine aggregate that changes with ambient temperature;

[0037] By collecting a large amount of measured data, the temperature change value △T of the cementitious material from the storage tank to before it is put into use is established. j1 The relationship model with the ambient temperature T0 is fitted to obtain the characteristic parameter n3 of the cementitious material changing with the ambient temperature:

[0038] △T j1 =|T j1 -T j0 |=|T j0 -T0|*[e^(-n3t)-1] (3)

[0039] in

[0040] △T j1 It is the temperature change from the incoming cementitious materials to the mixing plant before it is put into production;

[0041] T j1 It is the surface temperature of the cementitious material transported to the mixing plant before being put into use;

[0042] T j0 The temperature of the gelling material in the storage tank;

[0043] n3 is the characteristic parameter of the cementitious material that changes with ambient temperature.

[0044] Moreover, the specific process of step 5) is as follows:

[0045] According to formula (4), the amount of coarse aggregate Q c , belt conveyor speed v c , the mass M2 of coarse aggregate per meter on the conveyor belt, determines the time the coarse aggregate is cooled by wind, that is, the conveying time t2 of the belt conveyor:

[0046] Q c =v c t2M2 (4)

[0047] in

[0048] Q c is the amount of coarse aggregate;

[0049] v c The speed of the conveyor belt for transporting coarse aggregate;

[0050] t2 is the conveyor belt conveying Q c time required to mass coarse aggregate;

[0051] M2 is the mass of coarse aggregate per meter on the conveyor belt;

[0052] According to the coarse aggregate conveying time t2 on the belt conveyor, the target temperature T c2 , the air outlet temperature T of the cooling fan is calculated by formula (5) L0 ;

[0053] △T c2 =|T c2 -T c1 |=|T c1 -T L0 |*[ e^(-n1t2)] (5)

[0054] in:

[0055] △T c2 is the temperature change of coarse aggregate before and after air cooling;

[0056] T c2 is the target temperature of the coarse aggregate after air cooling;

[0057] T L0 The air outlet temperature of the air cooler.

[0058] Moreover, the specific process of step 6) is as follows:

[0059] According to formula (6), the target temperature T of the fine aggregate after cooling is x2, the mixing time of fine aggregate and cold water is t3, and the cold water temperature T is calculated. ld :

[0060] △T x2 =|T x2 -T x1 |=(T x1 -T ld )*[ e^(-n2t3)-1] (6)

[0061] in

[0062] △T x2 is the temperature change of fine aggregate after water cooling;

[0063] T x2 Cooling target temperature for fine aggregate;

[0064] T ld is the cold water temperature;

[0065] t3 is the mixing time of fine aggregate and cold water;

[0066] According to formula (7), the amount of fine aggregate Q x , the temperature of the mixture of fine aggregate and cold water T h , determine the cold water consumption Q ld :

[0067] Q ld (T h -T ld )=C x *|T x2 -T h |*Z*Q x (7)

[0068] in

[0069] C s is the specific heat capacity of water; Q ld For cold water usage;

[0070] C x is the specific heat capacity of fine aggregate; Q x is the amount of fine aggregate;

[0071] T h is the temperature of the mixture of fine aggregate and cold water;

[0072] Z is the ratio of the total mass of solid materials to the mass of fine aggregate in the mix.

[0073] Moreover, the specific process of step 7) is as follows:

[0074] According to formula (8), the temperature T of the gelling material after cooling isj2 , determine the mixing time t4 of the gelling material and the flake ice;

[0075] △T j2 =|T j2 -T j1 |=|T j1 -T b |*[ e^(-n3t4)] (8)

[0076] in

[0077] △T j2 It is the temperature change value of the gelling material after being cooled;

[0078] T j2 It is the temperature of the gelling material after it is cooled;

[0079] T b is the flake ice temperature, which is 0°C;

[0080] t4 is the mixing time of the gelling material and flake ice;

[0081] Substituting n3 into the adiabatic temperature rise as in formula (9) is used to adjust the adiabatic temperature rise of the hydration heat:

[0082] T t =Q j *Q / C h *ρ(1-e^(-n3mt)) (9)

[0083] in

[0084] T t is the maximum adiabatic temperature rise of concrete;

[0085] Qj is the amount of cementitious material used;

[0086] C h is the specific heat capacity of concrete;

[0087] ρ is the density of concrete;

[0088] m is the temperature coefficient, which changes with temperature. At 16°C, it is 0.35;

[0089] Q is the total hydration heat of cementitious materials, Q=kQ0, Q0 is the total hydration heat of cement, which is taken as 375, and k is the hydration heat adjustment coefficient of admixtures with different outputs;

[0090] According to the law of energy conservation, according to formula (10), the amount of cementitious material Q j , target temperature of concrete after cooling T m , determine the amount of flake ice used Q p ;

[0091] |T h+ T t -T m |*(Z2*Q j *C j +Q 1d *C s +Q P *C s ) = T m * Q j * C j (10)

[0092] The temperature of flake ice is considered to be 0 degrees Celsius here;

[0093] C j is the specific heat capacity of the gelling material;

[0094] Q j is the amount of cementitious material;

[0095] T m is the target temperature of the concrete after cooling, with a threshold of 16°C;

[0096] Z2 is the ratio of the total mass of solid materials to the mass of cementitious materials in the mix.

[0097] The advantages and beneficial effects of the present invention are:

[0098] 1. The present invention is applicable to a temperature control method for a large pre-cooling concrete mixing plant. By establishing a calculation model of the relationship between the temperature change value of coarse aggregate, fine aggregate and cementitious material from storage to before being put into use and the ambient temperature, the temperature characteristic parameters of the coarse aggregate, fine aggregate and cementitious material changing with the ambient temperature are obtained. Then, by constructing a model in each cooling step in the primary air cooling, ice adding and cold water adding refrigeration processes, the speed of the belt conveyor for transporting coarse aggregate, the air outlet temperature of the air cooler, the amount of cold water and the amount of flake ice used under different ambient temperatures are determined. The sensitivity factors of the materials to the ambient temperature are taken into consideration, so as to achieve the maximum saving of the pre-cooling equipment of the mixing plant production system under the premise of meeting the pre-cooling concrete outlet temperature requirement.

[0099] 2. The present invention is applicable to a temperature control method for a large pre-cooling concrete mixing plant. Through practical exploration, it is determined that under different natural ambient temperatures, when the pre-cooling concrete mixing plant produces different outlet temperature requirements, the air cooling time, air cooling temperature, amount of cold water and flake ice of the coarse aggregate can be effectively controlled. While meeting the outlet temperature requirements of the pre-cooling concrete, the maximum allocation of resources is achieved to the greatest extent, cost is saved, and efficiency is improved, which can further achieve the goal of a green, low-carbon, energy-saving and environmentally friendly pre-cooling concrete mixing plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] Figure 1The present invention is a flow chart of the temperature control method of a large-scale precooling concrete mixing plant. DETAILED DESCRIPTION

[0101] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0102] A temperature control method applicable to a large precooling concrete mixing plant, the temperature control method comprising the following steps:

[0103] Step 1) Determine the ambient temperature T0 at the mixing plant location;

[0104] Step 2) The coarse aggregate and fine aggregate are transported to the aggregate storage shed through the receiving silo and stored separately. The surface temperature T of the coarse aggregate is measured in the storage shed. c0 , fine aggregate surface temperature T x0 ; The cementitious material is stored in the tank and its surface temperature T is measured j0 ;

[0105] Step 3) Before concrete production begins, coarse aggregate and fine aggregate are transported to the mixing plant by a belt conveyor. The surface temperature of the coarse aggregate is measured as T before being put into use. c1 , the surface temperature of fine aggregate is T x1 ; Use pneumatic conveying to transport cementitious materials to the mixing plant. Before putting them into use, measure the surface temperature of the cementitious materials as T j1 ;

[0106] Step 4) By collecting a large amount of data from steps 1) to 3), a relationship model between the temperature change value of coarse aggregate, fine aggregate and cementitious material from storage to before being put into use and the ambient temperature is established, and the characteristic parameters of coarse aggregate, fine aggregate and cementitious material changing with ambient temperature are obtained by fitting.

[0107] The specific process of step 4) is as follows:

[0108] By collecting a large amount of measured data, the temperature change value △T of coarse aggregate from storage to before it is put into use is established. c1 The relationship model with the ambient temperature T0 can be fitted to obtain the characteristic parameter n1 of coarse aggregate changing with ambient temperature:

[0109] △T c1 =|T c1 -T c0 |=|T c0 -T0|*[e^(-n1t)-1] (1)

[0110] in,

[0111] △T c1It is the temperature change value of coarse aggregate from storage to before it is put into use;

[0112] T c1 The surface temperature of the coarse aggregate transported to the mixing plant before being put into use;

[0113] T c0 It is the surface temperature of coarse aggregate when it is stored in the storage shed;

[0114] T0 is the ambient temperature at the mixing plant location;

[0115] t is the time factor, which is 1 after normalization;

[0116] n1 is the characteristic parameter of coarse aggregate that changes with ambient temperature;

[0117] By collecting a large amount of measured data, the temperature change value △T of fine aggregate from storage to before it is put into use is established. x1 The relationship model with the ambient temperature T0 is fitted to obtain the characteristic parameter n2 of fine aggregate changing with ambient temperature:

[0118] △T x1 =|T x1 -T x0 |=|T x0 -T0|*[e^(-n2t)-1] (2)

[0119] in,

[0120] △T x1 It is the temperature change value of fine aggregate from storage to before it is put into use;

[0121] T x1 The surface temperature of fine aggregate transported to the mixing plant before being put into use;

[0122] T x0 It is the surface temperature of fine aggregate when it is stored in the storage shed;

[0123] n2 is the characteristic parameter of fine aggregate that changes with ambient temperature;

[0124] By collecting a large amount of measured data, the temperature change value △T of the cementitious material from the storage tank to before it is put into use is established. j1 The relationship model with the ambient temperature T0 is fitted to obtain the characteristic parameter n3 of the cementitious material changing with the ambient temperature:

[0125] △T j1 =|T j1 -T j0 |=|T j0 -T0|*[e^(-n3t)-1] (3)

[0126] in

[0127] △T j1 It is the temperature change from the incoming cementitious materials to the mixing plant before it is put into production;

[0128] T j1 It is the surface temperature of the cementitious material transported to the mixing plant before being put into use;

[0129] T j0 The temperature of the gelling material in the storage tank;

[0130] n3 is the characteristic parameter of the cementitious material that changes with ambient temperature.

[0131] Step 5) According to the relationship model between the amount of coarse aggregate, the transport speed of coarse aggregate, the air outlet temperature of the air cooler, the cooling temperature of coarse aggregate and the characteristic parameters of coarse aggregate changing with ambient temperature obtained in step 4), the conveying time of the belt conveyor for transporting coarse aggregate is obtained, and then the air outlet temperature of the air cooler is obtained;

[0132] According to formula (4), the amount of coarse aggregate Q c , belt conveyor speed v c , the mass M2 of coarse aggregate per meter on the conveyor belt, determines the time the coarse aggregate is cooled by wind, that is, the conveying time t2 of the belt conveyor:

[0133] Q c =v c t2M2 (4)

[0134] in

[0135] Q c is the amount of coarse aggregate;

[0136] v c The speed of the conveyor belt for transporting coarse aggregate;

[0137] t2 is the conveyor belt conveying Q c time required to mass coarse aggregate;

[0138] M2 is the mass of coarse aggregate per meter on the conveyor belt;

[0139] According to the conveying time t2 of the coarse aggregate on the belt conveyor, the cooling temperature T c2 , the air outlet temperature T of the cooling fan is calculated by formula (5) L0 ;

[0140] △T c2 =|T c2 -T c1 |=|T c1 -T L0 |*[ e^(-n1t2)] (5)

[0141] in:

[0142] △T c2 is the temperature change of coarse aggregate before and after air cooling;

[0143] T c2 is the target temperature of the coarse aggregate after air cooling;

[0144] T L0 The air outlet temperature of the air cooler.

[0145] Step 6) According to the relationship model between the fine aggregate dosage, the fine aggregate cooling temperature, the cold water temperature, the cold water dosage, the cooling temperature of the fine aggregate and the cold water mixture and the characteristic parameter of the fine aggregate changing with the ambient temperature, the cold water temperature, the cold water dosage Q are obtained. ld ;

[0146] According to formula (6), the target temperature T of the fine aggregate after cooling is x2 , the mixing time of fine aggregate and cold water is t3, and the cold water temperature T is calculated. ld :

[0147] △T x2 =|T x2 -T x1 |=(T x1 -T ld )*[ e^(-n2t3)-1] (6)

[0148] in

[0149] △T x2 is the temperature change of fine aggregate after water cooling;

[0150] T x2 Cooling target temperature for fine aggregate;

[0151] T ld is the cold water temperature;

[0152] t3 is the mixing time of fine aggregate and cold water;

[0153] According to formula (7), the amount of fine aggregate Q x , the temperature of the mixture of fine aggregate and cold water T h , determine the cold water consumption Q ld :

[0154] Q ld (T h -T ld )=C x *|T x2 -T h |*Z*Q x (7)

[0155] in

[0156] C s is the specific heat capacity of water; Q ld For cold water usage;

[0157] C x is the specific heat capacity of fine aggregate; Q x is the amount of fine aggregate;

[0158] T h is the temperature of the mixture of fine aggregate and cold water;

[0159] Z is the ratio of the total mass of solid materials to the mass of fine aggregate in the mix.

[0160] Step 7) establishing a relationship model between the amount of cementitious material used, the target value of concrete cooling temperature and the characteristic parameters of the cementitious material changing with the ambient temperature, and determining the amount of flake ice used;

[0161] The specific process of step 7) is as follows:

[0162] According to formula (8), the temperature T of the gelling material after cooling is j2 , determine the mixing time t4 of the gelling material and the flake ice;

[0163] △T j2 =|T j2 -T j1 |=|T j1 -T b |*[ e^(-n3t4)] (8)

[0164] in

[0165] △T j2 It is the temperature change value of the gelling material after being cooled;

[0166] T j2 It is the temperature of the gelling material after it is cooled;

[0167] T b is the flake ice temperature, which is 0°C;

[0168] t4 is the mixing time of the gelling material and flake ice;

[0169] n3 represents the characteristics of the cementitious material itself that are affected by temperature. However, since the cementitious material undergoes hydration heat reaction during the mixing process with water, the resulting adiabatic temperature rise is shown in formula (9). Therefore, n3 can be used to adjust the adiabatic temperature rise of hydration heat:

[0170] T t =Q j *Q / C h*ρ(1-e^(-n3mt)) (9)

[0171] in

[0172] T t is the maximum adiabatic temperature rise of concrete;

[0173] Qj is the amount of cementitious material used;

[0174] C h is the specific heat capacity of concrete;

[0175] ρ is the density of concrete;

[0176] m is the temperature coefficient, which changes with temperature. At 16°C, it is 0.35.

[0177] Q is the total hydration heat of cementitious materials, Q=kQ0, Q0 is the total hydration heat of cement, which is taken as 375, and k is the hydration heat adjustment coefficient of admixtures with different outputs, which can be obtained by looking up the following table;

[0178]

[0179] According to the law of energy conservation, the amount of cementitious material Q can be calculated according to formula (10): j , target temperature of concrete after cooling T m , determine the amount of flake ice used Q p ;

[0180] |T h +T t -T m |*(Z2*Q j *C j +Q 1d *C s +Q P *C s ) = T m * Q j * C j (10)

[0181] The temperature of flake ice is considered to be 0 degrees Celsius here;

[0182] C j is the specific heat capacity of the gelling material;

[0183] Q j is the amount of cementitious material;

[0184] T m is the target temperature of the concrete after cooling, with a threshold of 16°C;

[0185] Z2 is the ratio of the total mass of solid materials to the mass of cementitious materials in the mix.

[0186] Step 8) Optimize the cycle from step 4) to step 7) to determine the air outlet temperature of the air cooler, the cold water temperature, the cold water usage and the flake ice usage under different ambient temperatures.

[0187] The calculation example of the present invention is given below:

[0188] n1 is the characteristic parameter of coarse aggregate changing with ambient temperature, n2 is the characteristic parameter of fine aggregate changing with ambient temperature, and n3 is the characteristic parameter of cementitious material changing with ambient temperature. It can directly reflect the change of coarse aggregate, fine aggregate and cementitious material with ambient temperature under natural conditions, and provide data reference for the storage conditions of cementitious material in the production system. It can be obtained by fitting according to a large amount of measured data on site according to formula (1), formula (2) and formula (3). As shown in Table 1.

[0189] Table 1. Fitting of n1, n2, and n3

[0190]

[0191] According to the n1, n2, and n3 obtained by fitting in Table 1, they are substituted into formulas (4) to (9), and the outlet temperature of the mixing plant air cooler, the chilled water temperature, the amount of chilled water, and the amount of flake ice used can be comprehensively calculated under different ambient temperature conditions when the concrete outlet temperature is controlled below 16°C, see Table 2.

[0192] Table 2 Specific calculation examples

[0193]

[0194]

[0195]

[0196] In Example 1, the field measurement was conducted without using n1, n2, and n3 to correct the relevant formulas in formulas (4) to (9). When the ambient temperature of the mixing plant was 28°C, the parameter data under the set working conditions were collected. See Table 2 for the calculation results: the air outlet temperature of the air cooler was 10°C, the speed v of the belt conveyor for transporting coarse aggregate was c The speed is 1m / s; the cold water temperature is 8℃, the cold water consumption is 200kg; 50kg flake ice is added, and the final target temperature of the concrete after cooling is 14.5℃.

[0197] In Example 2, the relevant formulas in formulas (4) to (9) are revised by using n1, n2, and n3 of the present invention. After calculation, when the ambient temperature is 28°C, the parameter data under the set working condition are collected. Referring to Table 2, the following is calculated: the air outlet temperature of the air cooler is 10°C, the cold water temperature is 8°C, the cold water consumption is 200kg, 30kg of flake ice is added, and the final concrete outlet temperature is 16.0°C. The accurate prediction of the parameters to be controlled in the process is achieved, and at the same time, the usage of cold water and flake ice can be optimized, realizing the rational use of resources.

[0198] In Example 3, the field measurement was conducted without using n1, n2, and n3 to correct the relevant formulas in formulas (4) to (9). When the ambient temperature of the mixing plant was 32°C, the parameter data under the set working conditions were collected. See Table 2 for the calculation results: the air outlet temperature of the air cooler was 8°C, the speed of the belt conveyor for transporting coarse aggregate v c The speed is 1m / s; the cold water temperature is 8℃, the cold water consumption is 200kg; 40kg flake ice is added, and the final concrete outlet temperature is 15.6℃.

[0199] Example 4: The relevant formulas in formulas (4) to (9) are revised by using n1, n2 and n3 of the present invention. When the ambient temperature is 32°C, the parameter data under the set working condition are collected. See Table 2, and the following are calculated: the air outlet temperature of the air cooling is 8°C, the belt conveyor speed v for transporting coarse aggregate is c The speed is 1m / s; the cold water temperature is 8°C, the cold water consumption is 200kg, and 35kg of flake ice is added, which reduces the flake ice consumption by 12.5% ​​compared with Example 3. The final concrete outlet temperature is 15.4°C. The precise budget of the parameters to be controlled in the process is achieved, and at the same time, the consumption of chilled water and flake ice can be optimized, realizing the rational use of resources.

[0200] Example 5, using the present invention n1, n2, n3 to revise the relevant formulas in formula (4)-(9), when the ambient temperature is 32 ° C, collect the parameter data under the set working condition, refer to Table 2, and calculate: the air outlet temperature of the air cooling is 9 ° C, the belt conveyor speed v of the coarse aggregate transport is c 1m / s; cold water temperature 8℃, cold water consumption 200kg, 40kg flake ice added, the final concrete outlet temperature is 15.6℃, realizing the precise budget of the parameters to be controlled in the process, and at the same time, optimizing the use of chilled water and flake ice, realizing the rational use of resources. The air outlet temperature of air cooling is 9℃, which is 1℃ higher than that of Example 4. The air cooling system of the large concrete mixing plant in this example consists of 7 compressors and 8 air coolers, with a heat exchange area of ​​23,000㎡. For every 1℃ increase in temperature, 6,000 to 12,000 yuan / day in electricity can be saved.

[0201] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A temperature control method suitable for a large pre-cooling concrete mixing plant, characterized in that: The temperature control method comprises the following steps: Step 1) Determine the ambient temperature at the mixing plant location; Step 2) Determine the surface temperature of coarse aggregate and fine aggregate when stored in the storage shed and the temperature of cementitious material in the storage tank; Step 3) Determine the surface temperature of coarse aggregate, fine aggregate and cementitious materials in the storage shed and storage tank before they are transported to the mixing plant and put into use; Step 4) By collecting a large amount of data from steps 1) to 3), a relationship model between the temperature change values ​​of coarse aggregate, fine aggregate and cementitious material from storage to before being put into use and the ambient temperature is established, and characteristic parameters of coarse aggregate, fine aggregate and cementitious material changing with the ambient temperature are obtained by fitting; Step 5) According to the relationship model between the amount of coarse aggregate, the transportation speed of coarse aggregate, the air outlet temperature of the air cooler, the cooling temperature of coarse aggregate and the characteristic parameters of coarse aggregate changing with the ambient temperature obtained in step 4), the conveying time of the belt conveyor for transporting coarse aggregate and the air outlet temperature of the air cooler are obtained; Step 6) obtaining the cold water temperature according to the relationship model between the amount of fine aggregate, the cooling temperature of the fine aggregate, the cold water temperature, the amount of cold water, the cooling temperature of the mixture of fine aggregate and cold water and the characteristic parameters of the fine aggregate changing with the ambient temperature; Step 7) Determine the amount of flake ice to be used based on the relationship model between the amount of cementitious material used, the target value of concrete cooling temperature, and the characteristic parameters of the cementitious material changing with the ambient temperature. Step 8) Optimize the cycle from step 4) to step 7) to determine the air outlet temperature of the air cooler, the cold water temperature and the amount of flake ice used under different ambient temperatures; The specific process of step 4) is as follows: By collecting a large amount of measured data, the temperature change value of coarse aggregate from storage to before it is put into use is established. T c1 Relationship with ambient temperature T 0, the characteristic parameters of coarse aggregate changing with ambient temperature can be fitted n 1:△ T c1 =| T c1 - T c0 |=| T c0 -T 0 |* [ e^(-n 1 t)- 1] (1) Among them, △ T c1 It is the temperature change value of coarse aggregate from storage to before it is put into use; T c1 The surface temperature of the coarse aggregate transported to the mixing plant before being put into use; T c0 It is the surface temperature of coarse aggregate when it is stored in the storage shed; T 0 is the ambient temperature where the mixing plant is located; t is the time factor, which is normalized and takes 1 in calculation; n 1 is the characteristic parameter of coarse aggregate changing with ambient temperature; By collecting a large amount of measured data, the temperature change value of fine aggregate from storage to before it is put into use is established. T x1 With ambient temperature T 0, and the characteristic parameters of fine aggregate changing with ambient temperature are obtained by fitting n 2: (2) △ T x1 It is the temperature change value of fine aggregate from storage to before it is put into use; T x1 The surface temperature of fine aggregate transported to the mixing plant before being put into use; T x0 It is the surface temperature of fine aggregate when it is stored in the storage shed; n 2 is the characteristic parameter of fine aggregate changing with ambient temperature; By collecting a large amount of measured data, the temperature change value of the cementitious material from the storage tank to before it is put into use is established. T j1 With ambient temperature T 0, and fitted the characteristic parameters of the cementitious material changing with the ambient temperature. n 3 : （3） Among them T j1 It is the temperature change from the incoming cementitious materials to the mixing plant before it is put into production; T j1 It is the surface temperature of the cementitious material transported to the mixing plant before being put into use; T j0 The temperature of the gelling material in the storage tank; n 3 It is the characteristic parameter of cementitious material that changes with ambient temperature.

2. The temperature control method applicable to a large pre-cooling concrete mixing plant according to claim 1 is characterized in that: The specific process of step 5) is as follows: According to formula (4), the amount of coarse aggregate Q c , belt conveyor speed v c , the mass M2 of coarse aggregate per meter on the conveyor belt, determines the time the coarse aggregate is cooled by wind, that is, the conveying time t2 of the belt conveyor: Q c =v c t2M2 (4) in Q c is the amount of coarse aggregate; v c The speed of the conveyor belt for transporting coarse aggregate; t2 is conveyor belt conveyor Q c time required to mass coarse aggregate; M2 is the mass of coarse aggregate per meter on the conveyor belt; According to the coarse aggregate conveying time t2 on the belt conveyor, the target temperature of the coarse aggregate after air cooling T c2 , the air outlet temperature of the cooling fan is calculated by formula (5): T L0 ; △ T c2 =| T c2 - T c1 |=| T c1 - T L0 |*[ e^(- n 1 t 2)] （5） in: △ T c2 is the temperature change of coarse aggregate before and after air cooling; T c2 is the target temperature of the coarse aggregate after air cooling; T L0 The air outlet temperature of the air cooler.

3. The temperature control method applicable to a large pre-cooling concrete mixing plant according to claim 1 is characterized in that: The specific process of step 6) is as follows: According to formula (6), the target temperature of the fine aggregate after cooling is T x2 , the mixing time of fine aggregate and cold water is t3, and the cold water temperature is calculated T ld : △T x2 =|T x2 -T x1 |=（T x1 -T ld ）* [ e^(-n 2 t 3 )- 1]（6） in △T x2 is the temperature change of fine aggregate after water cooling; T x2 Cooling target temperature for fine aggregate; T ld is the cold water temperature; t3 is the mixing time of fine aggregate and cold water; According to formula (7), the amount of fine aggregate can be Q x , the temperature of the mixture of fine aggregate and cold water T h , determine the amount of cold water Q ld : Q ld （T h -T ld ）=C x *|T x2 - T h |*Z*Q x （7） in C s is the specific heat capacity of water; Q ld For cold water usage; C x is the specific heat capacity of fine aggregate; Q x is the amount of fine aggregate; T h is the temperature of the mixture of fine aggregate and cold water; Z is the ratio of the total mass of solid materials to the mass of fine aggregate in the mix.

4. The temperature control method applicable to a large pre-cooling concrete mixing plant according to claim 1, characterized in that: The specific process of step 7) is as follows: According to formula (8), the temperature of the gelling material after cooling is T j2 , determine the mixing time of the cementitious material and flake ice t 4; △T j2 =|T j2 -T j1 |=|T j1 -T b |* [ e^(-n 3 t 4 ) ]（8） in △T j2 It is the temperature change value of the gelling material after being cooled; T j2 It is the temperature of the gelling material after it is cooled; T b is the flake ice temperature, which is 0°C; t 4 is the mixing time of the gelling material and the flake ice; Will n Substituting the adiabatic temperature rise into formula (9) is used to adjust the adiabatic temperature rise of the hydration heat: T t = Q j *Q / C h * (1-e^(- n 3mt) (9) in T t is the maximum adiabatic temperature rise of concrete; Q is the amount of cementitious material; C h is the specific heat capacity of concrete; ρ is the density of concrete; m is the temperature coefficient, which changes with temperature. At 16°C, it is 0.35; Q is the total hydration heat of the cementitious material, Q=kQ 0 , Q 0 is the total heat of cement hydration, taken as 375, k is the adjustment coefficient of hydration heat of admixtures with different outputs; According to the law of energy conservation, according to formula (10), the amount of cementitious material is Q j , Target temperature of concrete after cooling T m , determine the amount of flake ice to use Q p ; |T h+ T t - T m |* （ Z 2 *Q j *C j +Q 1d *C s +Q P *C s ） = T m * Q j * C j （10） The temperature of flake ice is considered to be 0 degrees Celsius here; C j is the specific heat capacity of the gelling material; Q j is the amount of cementitious material; T m is the target temperature of the concrete after cooling, with a threshold of 16°C; Z 2 is the ratio of the total mass of solid materials to the mass of cementitious materials in the mix ratio.

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