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(с) Scientific-Engineering Center, 3R-Technology. naumir@yandex.ru, mirmov@hotmail.com, miily@yandex.ru

The technical and economic proposal

Cascade Refrigeration Machine of the Combined Type

Background

In the factories of meat, dairy and food industries are widely used freezers for shock freezing products of a large number of items. For quick freezing in the freezer is necessary to maintain a temperature of minus 35 - 40°C. In plants of biological preparation and some of chemical and petrochemical manufacturing there is a need for low temperature cold too. For achieving in freezers temperatures of minus 40 - 45°C refrigerants NH₃, R22, R502, R131b are used with employment, as a rule, two-stage refrigeration machines. At present for theses temperatures the two-stage ammoniac compressors machine using. For a freezer temperature below minus 45°C is used cascade refrigerating machines which use two or more refrigerants with different thermophysical properties. Cascade refrigeration machine consists of two single-stage refrigeration machines, called the upper and lower branch of the cascade.

The company "N.A.M. Technology "Ltd. It has developed and produced a working model of a cascade refrigeration machines combined type. A distinctive feature of this machine is that the machine consists of two single-stage refrigeration machines, in which the upper branch of the cascade is an absorption refrigeration machine, and the lower branch of the cascade - compression refrigeration machine. Such refrigeration machine consumes 55 - 60% less electricity than any refrigeration machine with two compressors or two-stage refrigeration machine which runs on ammonia or Freon.

On the developed cascade refrigeration machine of the combined type filed patent application [Application number US 14/706,246 of filling receipt 05/07/2015].

1. The main distinguishing features the cascade refrigeration machines of the combined type

1.1. Cascade refrigeration machine consists of two single-stage refrigeration machines: the upper branch of the cascade - absorption refrigeration machine, the lower branch of the cascade - compression refrigeration machine;

1.2. The upper branch of the cascade may be constructed as a two-stage absorption refrigeration machine that allows to obtain in the lower branch of the cascade the boiling temperature minus 70° - 75°C;

1.3. The upper branch of the cascade can be operated on the secondary heat sources as well as on primary heat sources (gas, boiler oil, wood waste);

1.4. The upper branch of the cascade - absorption refrigeration machine main apparatuses of which allow you to work on working solutions of substances: Freon / DME-TEG (Freon systems) or alcohol / LiCl, LiBr, ZnBr₂ (of alcohol systems);

1.5. The binding apparatus of the cascades the evaporator - condenser is done from the heat pipes or two-phase thermosyphons that improves the efficiency of heat transfer by 30 - 35%, and the reliability of at least twice;

1.6. For quick-freezing machines of shock freezing, the low-temperature freezing chamber with temperatures up to minus 35°C in the lower stage of the cascade is used quite the effective Freon 410A;

2. The basic advantages

2.1. In table 1 show the comparative characteristics the cascade refrigeration machine of the combined type with a standard refrigeration machine, which consists of two single-stage compression machines.

Table 1

		Q0	t0	Nc	Ns	N	Refrigerant	ε	Saving
		kW	^oC	kW	kW	kW			%
Cascade RM VCM / VCM	U-B	11.63		7.22	7.5	14.5	R22	1.4
	L-B		–70	6.53	7.0		R13
Cascade RM Combined type	U-B	11.63		0.7	1.5	8.5	R22	5.76	41.4
	L-B		–70	6.53	7.0		R410A

The upper branch of the cascade is provided with a circulation pump with an engine of 0.7 kW. Given the capacity of the pump for hot water (flow to the generator) and cold water (flow to the condenser and the absorber), the total installed capacity of the pumps will be 1.5 kW.

In table 2 show comparative characteristics cascade refrigeration machine of the combined type with the standard two-stage refrigeration machine.

Table 2

		Q0	t0	Nec	Nic	Ntp	Refrigerant	ε	Saving
		kW	^oC	kW	kW	kW			%
Two-stage RM	Hp-S	93.0	–40.83	22.3	23.5	52.0	NH3	3.01
	Lp-S			26.3	28.5.0		NH3
Cascade RM Сombined type	U-B	93.0	–49.68	4.0	4.5	30.0	R22	5.76	42.3
	L-B			23.33	25.5		R410A

Notation convention in the tables: Cascade RM – cascade refrigeration machine; Combined type – combined type; VCM – vapor compression machine; Two-stage RM – two-stage compression machine; U-B – upper branch of cascade; L-B – lover branch of cascade; Hp-S – high-pressure stage; Lp-S – low-pressure stage; Q₀ – refrigerating capacity; t₀ – boiling temperature in the evaporator; N_ec – effective capacity; N_ic – installed capability; N_tp – total power; ε – energy efficiency ratio;

2.2. Replacement of two-stage ammonia refrigerating machines by cascade machines of combined type, in which safe refrigerants in every respect are used, such as Freon 410A increases the operational safety of refrigerating units.

2.3. In the cascade type refrigerating machine of combined type considering ultimate temperature difference between boiling and condensation in the evaporator - condenser 5°C, energy efficiency ratio of the cascade machine will be ε_с = 5.76.

2.4. At boiling temperature in the evaporation circuit of evaporator - condenser from minus 6°C up to minus 19°C (depending on the used refrigerant in the upper branch of the cascade), the temperature in the freezer reaches minus 46.5°C, while compressor discharge pressure of the lower branch of the cascade is not greater than 5.8 bar and the temperature of overheating at the compressor outlet is not more than 60 - 64°C.

2.5. The conversion factor of heat (COP) value in an absorption refrigerating machine of the upper branch of the cascade for the working solution R22 / DME-TEG is 0.69 - 0.71. For a working solution based on alcohol / LiBr COP value of is around 0.8 - 0.82. The COP value depends on the initial temperature of the heating source and the heat load of the evaporator - condenser.

3. Fields of application of the cascade refrigeration machine

3.1. The main consumers of cascade refrigeration machines are plants of meat and fish industry, chemical and petrochemical industry, production of ice cream and fast frozen fruits and vegetables;

3.2. The factories for biological preparations, in scientific institutions, that require low temperature cold (about minus 70 - 80°C)

4. The economic expediency of the use and manufacture of cascade refrigeration machines

4.1. For the enterprise developer and manufacturer

4.1.1. Market demand for refrigeration machines depends on the possibility of obtaining a low temperature in the freezing or refrigerating chamber at lower electrical energy consumption. Depending on the volume of production and technological equipment manufacturer may recommend the following series of cascading machines:

- The temperature in the cooling volume minus 70° - 80°, a performance of 10 - 30 kW;

- The temperature in the freezer to minus 30 - 44°C, a performance of 80 - 350 kW

If cascade machines of productivity 1,000 kW and higher will be in demand, they will equipped with a set of identical machines with the required total productivity.

4.1.2. The manufacturer should organize contract supervision and start-up commissioning to assist in the maintenance. This will allow the company to increase revenues by 45 - 50%.

4.2. For a company or enterprise that acquires cascade refrigeration machine of combined type, economic efficiency is made up of the following activities:

4.2.1. The acquisition and operation of the cascade refrigerating machine instead one of a two-stage ammonia refrigeration machines (see options in section 2, paragraph 2.2), the annual energy saving is about 153,144 kWh.

4.2.2. The maintenance of the one cascade machine of combined type (parameters - see Section 2, paragraph 2.1) within a year will save 36,144 kWh.

4.2.3. Using cascade machines of combined type with harmless Freon instead of ammonia refrigerating machines reduces the cost of safety engineering and fire safety by 55 - 60%.

4.2.4. Using cascade machines of combined type with harmless Freon instead of ammonia refrigerating machines reduces the cost of social insurance and payments for maintenance personnel for harmful conditions of the operation of ammonia units.

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