WO2008053170A1

WO2008053170A1 - Non-ozone depleting refrigerant composition for centrifugal chillers

Info

Publication number: WO2008053170A1
Application number: PCT/GB2007/004090
Authority: WO
Inventors: John Edward Poole; Richard Powell
Original assignee: Rpl Holdings Limited
Priority date: 2006-10-28
Filing date: 2007-10-26
Publication date: 2008-05-08
Also published as: GB0621501D0

Abstract

Non ozone depleting refrigerant compositions which replace CFC12 in centrifugal chillers and are compatible with traditional lubricants (eg mineral and alkylbenzene oils) and also synthetic oxygen containing lubricants. Such refrigerant compositions are non flammable according to ASHRAE Standard 34.

Description

NON-OZONE DEPLETING REFRIGERANT COMPOSITION FOR CENTRIFUGAL CHILLERS

The refrigerant compositions which are the subject of this invention comprise mixtures of hydrofuorocarbons (HFCs) with small amounts of hydrocarbons. While it is well known that HFCs can replace Ozone Depleting Substances (ODS) such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), HFCs are not miscible with traditional lubricants (eg mineral and alkylbenzene oils) and must be used with synthetic oxygen containing lubricants (eg polyol ester and poly alkylbenzene oils) in order to achieve the required oil return to the compressor essential to the operation of a refrigeration unit. This invention relates to refrigerant compositions which can replace ODS with minor or in some cases no changes to the existing equipment while achieving the required level of oil circulation throughout the refrigeration system which is fundamental to its safe and satisfactory operation.

This invention relates to refrigerant compositions which can be retrofitted into centrifugal chillers to replace CFC 12 without the need to change the existing lubricant or make any changes to the hardware. The refrigerant composition has no ability to deplete the ozone layer and is further suitable for use in new equipment with synthetic oxygen containing lubricants.

While HFC 134a has a lower molecular weight than CFC 12, the molecular weight of HFC227ea is considerably higher than that of CFC 12 with the result that blends of these two HFC components can be made to match the molecular weight of CFC 12; this being an important property of any replacement for CFC 12 in centrifugal chillers.

HFC227ea finds application as an industrial fire extinguishant and also combines with butane to avoid flammable mixtures. HFC 125 is present to increase capacity while also being a fire suppressant. Butane is a core component of the composition by facilitating oil return to the compressor.

A key aspect of this invention is that while the inclusion of HFCs in the refrigerant compositions ensures low toxicity and a zero Ozone Depletion Potential (ODP), the addition of a hydrocarbon within the defined ranges enables a non flammable designation of Al to be achieved as defined by ASHRAE (American Society for Heating Refrigeration and Air conditioning Engineers) Standard 34. Preferred embodiments of this invention relate to refrigerant compositions comprising a hydrocarbon with HFC 134a, HFC 125 and HFC227ea which are non flammable when fractionated under leakage tests specified under ASHRAE Standard 34 and Underwriters Laboratories UL2182.

A flammability test according to ASHRAE Standard 34 was carried out by an independent laboratory on an estimated worst case fractionated formulation of a blend containing HFC 134a, HFC227ea, HFC 125 and butane with the results shown in example 1. Surprisingly it has been found that despite the presence of significant quantities of the fire suppressants HFC227ea and HFC 125 (both of which find application as fire extinguishants) with non flammable HFC 134a, a comparatively small amount of hydrocarbon present in the blend produces a flammable mixture at worst case fractionation.. This invention relates to refrigerant blends containing HFC134a, HFC125, HFC227ea and less than 2% butane which are non flammable according to ASHRAE Standard 34 and suitable as replacements for CFC 12 in centrifugal chillers.

The presence of a hydrocarbon promotes oil return to the compressor enabling traditional lubricants such as mineral and alkylbenzene oils to be used in either existing or new equipment. The selection of a hydrocarbon with HFCs in accordance with the invention enables non flammability of the blend to be achieved as defined by ASHRAE Standard 34.

Various terms have been used in patent literature to describe refrigerant mixtures. The following definitions are taken from ASHRAE Standard 34;

Azeotrope: an azeotropic blend is one containing two or more refrigerants whose equilibrium vapour and liquid phase compositions are the same at a given pressure. Azeotropic blends exhibit some segregation of components at other conditions. The extent of the segregation depends on the particular azeotrope and the application.

Azeotropic temperature: the temperature at which the liquid and vapour phases of a blend have the same mole fractionation of each component at equilibrium for a specified pressure.

Near azeotrope: a zeotropic blend with a temperature glide sufficiently small that it may be disregarded without consequential error in analysis for a specific application. Zeotrope: blends comprising multiple components of different volatilities that, when used in refrigeration cycles, change volumetric composition and saturation temperatures as they evaporate (boil) or condense at constant pressure.

Temperature glide: the absolute value of the difference between the starting and ending temperatures of a phase-change process by a refrigerant within a component of a refrigerating system, exclusive of any subcooling or superheating. This term usually describes condensation or evaporation of a zeotrope .

According to the present invention a refrigerant composition which is non flammable as defined by ASHRAE Standard 34 comprises:

R134a 60-48.1%

R227ea 37-45%

R125 2-5%

Butane 1-1.9% eferred embodiment compri

R134a 57-49.5%

R227ea 39-44%

R125 3-5%

Butane 1-1.5% ore preferred refrigerant cor

. Rl 34a 52.5%

R227ea 41%

R125 5%

Butane 1.5%

An especially preferred refrigerant composition comprises:

Rl 34a 53%

R227ea 41%

R125 4.5% Butane 1.5%

Yet another preferred refrigerant composition comprises

Rl 34a 52%

R227ea 42.5%

R125 4%

Butane 1.5%

Another preferred refrigerant composition comprises

Rl 34a 52%

R227ea 43.5%

R125 3%

Butane 1.5%

The invention further provides a centrifrugal chiller including a refrigerant in accordance with previous aspects of this invention, together with a lubricant. In a first preferred embodiment, the lubricant is a mineral oil or alkylbenzene or synthethic hydrocarbon lubricant. In a second embodiment, the lubricant is a synthetic oxygen- containing lubricant. In a third embodiment, the lubricant is a polyolester lubricant. In a fourth embodiment, the lubricant is a polyether lubricant. In a fifth embodiment, the lubricant is a mixture of oxygen-containing lubricants. In a sixth embodiment, the lubricant is a mixture of hydrocarbon and oxygen-containing lubricants.

The invention is further described by means of examples but not in a limitative sense.

In these examples the following abbreviations are employed.

AF As formulated blend composition

WCF Worst Case Formulation: the WCF is defined as the composition containing the highest (percentage) flammable components within the manufacturing tolerance range and the lowest amount of non flammable component. WCFF Worst Case Fractionated Formulation: when a blend undergoes a leak from a package or system, one or more flammable components may concentrate in the liquid or vapour phases due to fractionation. In order to evaluate properly the possible flammability risk of a blend the worst case formulation (WCF) composition is submitted to a standard leak test as specified by the ASHRAE 34 protocol. This leak test can either be experimental or simulated using a computer program such as NIST' s Refleak.

Example 1

The worst case fractionated formulation of a blend of HFC134a, HFC125, HFC227ea, and n-Butane was identified as follows:

%

Component AF WCF WC

HFC 134a 50 51.9 57.3

HFC227ea 41 40.0 31.4

HFC 125 6 5.0 6.9 n-Butane 3 3.1 4.4

A flammability test on a sample of the WCFF was conducted at 60⁰C according to ASTM 681-98 under ASHRAE Standard 34. The sample was found to be flammable with a Lower Flammable Limit of 9% (v/v).

Example 2

A centrifugal chiller operating under the conditions indicated below was simulated using NIST' s Cycle D program opera.

System cooling capacity 100 kW Compressor isentropic efficiency 0.7 Evaporation temperature O ⁰C Condensing temperature 35 ⁰C Evaporator superheat 7 ⁰C Condenser subcooling 5 ⁰C

Suction line pressure drop expressed as bubble point loss 1.5⁰C Discharge line pressure drop expressed as dew point loss 1.5⁰C Effectiveness of liquid line/suction line heat exchanger 0.3

The results for 9 different refrigerant blends and for Rl 2 are shown in Table 1.

Table 1

Claims

1. A refrigerant composition as consisting essentially of

R134a 60-48.1%

R227ea 37-45%

R125 2-5%

Butane 1-1.9%

2. A refrigerant composition as claimed in claim 1 consisting essentially of

Rl 34a 57-49.5%

R227ea 39-44%

R125 3-5%

Butane 1-1.5%

3. A refrigerant composition as claimed in claim 1 consisting essentially of

R134a 52.5%

R227ea 41%

R125 5%

Butane 1.5%

4. A refrigerant composition as claimed in claim 1 consisting essentially of

R134a 53%

R227ea 41%

R125 4.5%

Butane 1.5%

5. A refrigerant composition as claimed in claim 1 consisting essentially of

Rl 34a 52%

R227ea 42.5%

R125 4%

Butane 1.5%

6. A refrigerant composition as claimed in claim 1 consisting essentially of

Rl 34a 52%

R227ea 43.5%

R125 3%

Butane 1.5%

7. A refrigerant composition as claimed in any of claims 1 to 6, which meets the criteria for safety classifications Al and A2 of ASHRAE Standard 34.

8. A refrigerant composition as claimed in any of claims 1 to 6, which meets the criteria for safety classification Al of ASHRAE Standard 34.

9. A refrigerant composition as claimed in any of claims 1 to 6, which when allowed to leak under conditions specified by ASHRAE Standard 34 does not generate liquid or vapour mixtures with hydrocarbon contents greater than 1.9 weight %.

10. A refrigerant composition as claimed in any of claims 1 to 6, which when allowed leak under conditions specified by ASHRAE Standard 34 does not generate liquid or vapour mixtures with hydrocarbon contents greater than 1.5 weight %.

11. A refrigerant composition as claimed in any preceding claim, in which the weight percent of hydrocarbon does not vary more than 0.5% when the compositions under isothermal vapour leaks at 23⁰C.

12. A centrifugal chiller unit including a refrigerant as claimed in any of claims 1 to 11, together with a mineral oil, alkylbenzene or synthetic hydrocarbon lubricant.

13. A centrifugal chiller unit including a refrigerant as claimed in any of claims 1 to 11₅ together with a synthetic oxygen-containing lubricant.

14. A centrifugal chiller unit including a refrigerant as claimed in any of claims 1 to

11₅ together with a polyol ester lubricant.

15. A centrifugal chiller unit including a refrigerant as claimed in any of claims 1 to 11, together with a polyether lubricant.

16. A centrifugal chiller unit including a refrigerant as claimed in any of claims 1 to 11, together with a lubricant comprising a mixture of oxygen-containing lubricants.

17. A centrifugal chiller unit including a refrigerant as claimed in any of claims 1 to

11, together with a lubricant comprising a mixture of hydrocarbon and oxygen- containing lubricants.