RU2475684C1 - Ice-containing pulp obtaining method - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: ice-containing pulp is obtained by cooling the sea water until clathrate pulp is formed, by adding to the sea water of liquid CO₂ in the ratio of 1:1.6 at the temperature of 2°C below zero and at the pressure of 3.3 MPa, with its further removal at pressure reduction to 0.1 MPa to the storage reservoir.

EFFECT: increasing energy efficiency of the method for obtaining ice-containing pulp.

3 dwg

Description

The invention relates to refrigeration, in particular to methods for producing ice-containing pulps or suspensions, and can be used to cool and preserve fish raw materials directly on ships in the fishing area.

A known method of producing an ice-containing suspension, according to which the saline solution is cooled until water ice is formed on the inner surface of the evaporator generator, is made in the form of a horizontal cylindrical pipe, on the outside of which a pump is pumped with a coolant having a temperature below the solution crystallization point. The formed water ice is removed by means of a screw from the heat exchange surface to the storage tank. In the storage tank, crushed ice is mixed with the liquid phase of the initial solution to the state of an ice-containing pulp, which is then pumped to the storage tank [Bel O., Lallemand A., 1999, Etude d'un fluide frigoporteur diphasique - 2: Analyze expérimentale du comportement thermique et rhéologique, International Journal of Refrigeration, vol. 22, pp. 175-187].

The main disadvantage of this method is that the ice layer released on the heat exchange surface of the generator-evaporator is a thermal resistance that prevents the passage of heat flow from the crystallizing solution to the refrigerant. A device that removes ice from the heat exchange surface has a limited service life, because ice has high strength and roughness. In addition, the rotation of the device requires energy reaching 10% of the energy required to drive the compressor of the refrigeration unit, which removes heat from the crystallizing solution.

Closest to the claimed method is a method for producing an ice-containing pulp by cooling sea water to form water ice. Water ice is frozen on the vertical surface of the evaporator generator, made in the form of a plate and having a temperature below the cryoscopic point of the solution. After the formation of a thin layer of water ice on the surface of the evaporator plate, the boiling of the refrigerant in the evaporator ceases and hot steam is supplied to the evaporator cavity, which leads to the fall of the ice layer into the storage tank. In the storage tank, the ice is destroyed by a mechanical type device and mixed with the liquid phase of the initial solution to the state of an ice-containing pulp, after which the pulp is pumped to the storage tank (“A METHOD AND APPARATUS FOR PRODUCING HOMOGENOUS FLUID ICE.” WO / 2004/081469. Priority date 03/10/2003 Authors: ARNASON, Ingolfar; SIMONSSEN, Johannes; KRISTJANSSON, Theodor).

The disadvantage of this method is the high specific energy consumption for obtaining an ice-containing pulp. A mechanical type device for breaking ice and mixing it with the liquid phase of the initial solution to the pulp state is difficult to operate and has a high cost, and also requires high energy costs for its drive, which reach 10% of the compressor cooling capacity.

The objective of the invention is to reduce specific energy consumption for producing ice-containing pulp.

The problem is solved in that in the method for producing an ice-containing pulp, including cooling sea water in a generator-evaporator with subsequent removal of the resulting ice-containing pulp in a storage tank, according to the method, cooling is carried out until a clathrate pulp is formed by introducing liquid CO ₂ in sea water in a ratio of 1 : 1.6 at a temperature of minus 2 ° С under a pressure of 3.3 MPa, with its subsequent discharge when the pressure drops to 0.1 MPa into the storage tank, to use the pulp as a coolant to save fish s.

The technical result of the invention is to increase the energy efficiency of the method of producing ice-containing pulp.

The reduction of energy consumption for obtaining an ice-containing pulp is ensured by the fact that when the method is implemented, energy losses are eliminated in order to overcome the thermal resistance, which is the heat exchange surface between the refrigerant and the resulting clathrate pulp. In the inventive method, with direct contact of boiling CO ₂ with seawater, the heat energy of clathrate formation is removed at the lowest possible thermal resistance, which provides a temperature difference between boiling CO ₂ and the resulting clathrate pulp of 0.2 ° C. The heat necessary for the dissociation of clathrate pulp is supplied from crystallizing sea water also at the minimum possible temperature difference of 0.2 ° C. Thus, the proposed method for producing ice-containing pulp requires little energy, since all the processes taking place in this method are carried out as a result of interphase energy exchange.

CO ₂ , which is part of the clathrate pulp, is also a refrigerant. Since the boiling CO ₂ directly in contact with sea water and formed clathrate, its boiling point is substantially equal to the temperature of clathrate formation. In the contact type method, which is the claimed method, the temperature difference between the media due to their direct contact does not exceed 0.2-0.4 ° C (Desalination and Water Purification Research and Development Program Final Report No. 78. Mechanical Engineering University of Nevada Reno. November 2003). It is known that during the operation of vapor compression refrigeration units, an increase in the temperature difference between the boiling point of the refrigerant and its condensation temperature by 1 ° C increases the energy consumption by an average of 3.5% (Bambushek E.M., Bukharin N.N., Gerasimov E.D. . et al. / Under the general editorship of IA Sakun. Thermal and structural calculations of refrigeration machines: A textbook for universities in the specialty "Refrigeration machines and installations." - L.: Mechanical Engineering, 1987. - 423 p.). In similar methods for producing ice-containing pulp, the boiling point is 10 ° C lower than in the proposed method, therefore, the energy consumption in them will be higher by 35%.

The invention is illustrated in the graphic materials presented in figures 1-3, where

Figure 1 presents a diagram of the thermodynamic state of the clathrate H ₂ O-CO ₂ in the coordinates of pressure - temperature.

Figure 2 presents a diagram of the cycle of the refrigeration machine in the coordinates of pressure-enthalpy.

Figure 3 presents the technological scheme for producing ice-containing pulp.

и область, где клатрат Н₂O-СO₂ не может существовать

The diagram (figure 1) shows the process of formation of clathrate H ₂ O-CO ₂ in the generator-evaporator, as well as the region of steady state of clathrate

and the area where the clathrate of H ₂ O-CO ₂ cannot exist

+Клатрат), т.е. происходит процесс клатратообразования. Точки Q1 и Q2 на диаграмме являются инвариантными точками состояния клатрата, координаты которых определены из таблицы.In the plot of the diagram (Fig. 1), located to the right of the equilibrium line, sea water - clathrate, the sea water is cooled at the inlet to the generator-evaporator due to the boiling of liquid CO ₂ . With a decrease in water temperature from 8 ° С to minus 2 ° С, the point of its state crosses the equilibrium line and enters the region of clathrate existence (

+ Clathrate), i.e. the process of clathrate formation occurs. Points Q1 and Q2 in the diagram are invariant points of state of the clathrate, the coordinates of which are determined from the table.

The table shows the coordinates of the displacement of the invariant points Q1 and Q2 on the state diagram of the Н ₂ O-СО ₂ clathrate depending on water salinity (Larryn W. Diamond "Salinity of multivolatile fluid inclusions determined from clathrate hydrate stability" Bern, Switzerland, 1993).

Q1 Q2 Pure water - CO ₂ P-1.26 MPa; t - 0,0 ° C P-4.50 MPa; t - "+ 10.0 ° C" Sea water - CO ₂ P-1.12 MPa; t - "-2.0 ° C" P-4.00 MPa; t - "+ 8.0 ° C"

The results of studies of clathrate formation in sea water showed that the kinetics of the formation of all clathrates (water-butane, water-methane, water-ethane, water-carbon dioxide) in sea water is higher compared to the kinetics of processes in pure water.

The diagram (Fig. 1) at points 1-4 shows the refrigeration cycle of the generator-evaporator, in which the clathrate Н ₂ O-СО _{2 is formed} due to the removal of the heat of clathrate formation by boiling СО ₂ . During the implementation of the refrigeration cycle, CO ₂ vapor is discharged by the compressor (point 1), compressed to a pressure of 6 MPa (point 2), condenses into liquid in the condenser (segment at points 2-3), in the control valve, the pressure of liquid CO ₂ drops sharply from 6 to 3.3 MPa (segment at points 3-4) and at a pressure of 3.3 MPa, liquid CO ₂ boils at a temperature of minus 2 ° C (segment at points 4-1). At point 4, with the coordinates ("3.3" and "-2"), clathrate formation occurs. Leaving the region of its stable thermodynamic state (segment at points 4-5), the Н ₂ O-СО ₂ clathrate begins to dissociate into liquid Н ₂ O and gaseous CO ₂ with absorption of dissociation heat equal to 380 kJ / kg.

The source of heat for the dissociation process in a thermally insulated storage tank is liquid sea water located on the liquid – ice balance line at a temperature of minus 2 ° С and a pressure of 0.1 MPa. Sea water crystallizes with the release of thermal energy of 335 kJ / kg, providing dissociation (destruction) of the clathrate H ₂ O-CO ₂ , which takes place with the absorption of thermal energy of 380 kJ / kg. Moreover, due to the difference in the values of thermal effects during the dissociation of 1 kg of clathrate Н ₂ O-СО ₂ , 1.13 kg of water ice is formed (380/335 = 1.13), due to which the clathrate slurry “clathrate - sea water” with a content of 50 % clathrate passes into 57% ice-containing pulp.

Figure 2 presents the cycle of the refrigeration machine, which removes the heat of clathrate formation in the generator-evaporator. Point 1 corresponds to the inlet of vaporous СО ₂ to the compressor with a pressure of 3.3 MPa, point 2 corresponds to the outlet of vaporous CO ₂ from the compressor with a pressure of 6 MPa, the segment at points 2-3 displays the process of condensation of vaporous CO ₂ , i.e. transition to a liquid state. The segment at points 3-4 corresponds to a sharp decrease in the pressure of liquid CO ₂ in the control valve from 6 to 3.3 MPa. The 4-1 "process corresponds to the boiling of liquid CO ₂ in a generator-evaporator at a pressure of 3.3 MPa and a temperature of minus 2 ° С. The process 1" -1 corresponds to the overheating of vaporous СО ₂ from a temperature of minus 2 ° С to 10 ° С before entering compressor.

From the diagrams (figures 1, 2) it follows that at the point of the thermodynamic state of the mixture of sea water and liquid CO ₂ , a clathrate of H ₂ O + CO _{2 is formed} . Since, as a result of direct contact of boiling CO ₂ and the H ₂ O-CO ₂ clathrate resulting from this, the temperature difference between these processes does not exceed 0.2 ° С, the energy consumption for the implementation of the refrigeration cycle will be extremely close to its theoretical minimum, while as with the conventional method of heat removal, the temperature difference is 10 ° C, which leads to an increase in energy consumption by 35%.

In determining the proportion of seawater: CO ₂ it was considered that the two components are included in the clathrate in a ratio of 1: 1.6, is not completely transformed into a clathrate. At the indicated ratio, a pulp is formed in the evaporator generator, consisting of 50% clathrate and 50% seawater in liquid form. With a larger amount of clathrate in water, the pulp increases its viscosity above the limit value, which does not allow pumping it through pipelines.

A method of obtaining an ice-containing pulp is carried out on the installation, the technological scheme of which is shown in figure 3

The installation consists of a pump for supplying sea water 1, an evaporator-generator 2, compressor 3, a condenser 4, control valves 5, 6, a heat exchanger 7, an ice storage pulp storage tank 8.

The method is as follows.

When implementing the method, it is necessary to take into account that part of CO _{2 is} used as a refrigerant and its vapor after evaporation is removed by the compressor from the generator-evaporator to the condenser so that it returns to the cycle after condensation.

To obtain 1000 kg of ice-containing pulp, 830 kg of sea water is pumped into the generator-evaporator 2 using pump 1. Through the control valve 5, liquid CO _{2 is} supplied from the cylinder to the generator-evaporator 2 in the amount of 1332 kg. Due to the operation of the compressor 3 in the generator-evaporator 2 create and maintain a pressure of 3.3 MPa. Under these conditions, in the generator-evaporator 2, liquid CO ₂ is mixed with seawater, boils, while the temperature of the sea water drops to minus 2 ° С. The steam generated at the boiling of CO ₂ in an amount of 1162 kg is removed by compressor 3 to condenser 4. At a pressure of 3.3 MPa and a temperature of minus 2 ° C, a clathrate pulp is formed in the generator-evaporator 2, consisting of sea water and clathrate Н ₂ O- CO ₂ . Through the control valve 6, the clathrate pulp is released from the generator-evaporator 2 into the storage tank 8, while the pressure in the control valve 6 is reduced from 3.3 to 0.1 MP. Passing through the control valve 6, the clathrate pulp (dissociates) is destroyed and turns in the storage tank 8 into an ice-containing pulp saturated with gaseous carbon dioxide. In the storage tank 8, the ice-containing pulp is stored until the fish enter it.

The ice-containing pulp obtained by the method consists of 57% aqueous ice and 43% saline.

When the fish is immersed in the resulting ice-containing pulp, the fish is cooled to a temperature of minus 1 ° C when melting crystals of ice-containing pulp at a temperature of minus 2 ° C with an intensity of 5000-7000 W / m ² K.

The proposed method for producing ice-containing pulp avoids the use of complex and expensive devices that consume up to 10% of the electric power from the refrigeration compressor compressor. The complexity, cost and energy costs of conventional ice-pulp generators are due to the phenomenon of ice formation on the heat exchange surface, which separates boiling refrigerant and crystallized sea water in the evaporator. In the proposed method, the heat transfer surface in the evaporator-generator is absent, because the heat of clathrate formation from the resulting clathrate pulp is removed by boiling liquid CO ₂ due to interfacial energy exchange with direct, direct contact. There is no heat exchange surface in the storage tank of the ice-containing pulp, where it forms after the pressure in the control valve decreases.

Compared with the known technical solutions, the proposed method allows to increase the efficiency of obtaining ice-containing pulp by reducing the cost of electricity from 10 to 2% of the compressor cooling capacity. In this case, an ice-containing pulp will be obtained in a simple-by-design device with a small-capacity refrigeration unit during the transition of the vessel to fishing. For example: in order to cool 500 tons of fish from 10 ° C to minus 1 ° C in 4 hours, an ordinary pelagic trawler must have a refrigeration unit with a cooling capacity of 3500 kW, which consumes, depending on the operating mode, from 1000 to 1500 kW of electricity. When using cold accumulators, such as clathrate and ice-containing pulps, it is possible to equip fishing vessels with refrigeration units of much lower cooling capacity, because cold energy will be accumulated in the form of pulp during the transition of the vessel to the fishing area.

Claims (1)

A method of producing an ice-containing pulp, comprising cooling sea water in a generator-evaporator, followed by removal of the resulting ice-containing pulp into a storage tank, characterized in that the cooling is carried out until clathrate pulp is formed by introducing liquid CO ₂ in sea water in a ratio of 1: 1.6 at a temperature minus 2 ° С under a pressure of 3.3 MPa, with its subsequent discharge when the pressure drops to 0.1 MPa into the storage tank, to use the pulp as a coolant to save fish.

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