Ammonia Detection in Cooling & Refrigeration

Application

CoolingRefrigeration is used throughout industry wherever there is a need to maintain a product or process at a defined level. Compressing a refrigerant gas and then allowing it to evaporate carries out this cooling process. Several gases can be used to perform this action, natural gases such as Ammonia and Carbon Dioxide or a manufactured range of gases known as Freons. For many years Freons (CFCs and HCFCs) were seen as ideal clean, non-toxic, odourless etc., however it was discovered that CFCs cause depletion of the ozone level and are therefore banned. Their replacements, whilst causing less harm to the ozone layer, have a high global warming potential. In some cases, 100 times that of CO2. These gases are controlled by legislation known as F Gas regulations thus placing strict limits on the use of these gases and the necessity to detect them.

Ammonia has been used for over a century as refrigeration gas and has no global warming potential or effect on the ozone level. The drawback of Ammonia is that it is very toxic with a pungent odour and, in high concentrations, can be flammable. While this gas is not controlled by F Gas regulations, it is certainly subject to DSEAR regulations. The main thrust of the DSEAR regulations is to control the use of dangerous substances and gases in the work place. Therefore, an automatic Ammonia detection system must be in place.

Typical market segments are as follows:

  • Breweries
  • Food and Drink production
  • Storage
  • Abattoirs
  • Shipping (LPG / LNG vessels)
  • Rail and Road Transport
  • HVAC
  • Commercial and Domestic buildings
  • Cooling for IT systems (Finance Houses etc.)
  • Education and Sport facilities
  • Colleges
  • Laboratories
  • Ice Rinks
  • Chemical / Petrochemical industries
  • Pharmaceuticals

Problem

There are at least four different applications resulting from cooling and refrigeration with ammonia:

  1. The protection of personnel on site. Workers and visitors to a site using Ammonia as a refrigerant must be protected from the effects of ammonia on health and safety. Both portable and fixed instruments, or a mixture of both, can be used and are dependant on site conditions for this. Alarms need to be set at the Threshold Limit Value (TLV) of the regional regulation. The UK alarm values would normally be STEL 35ppm and LTEL 25ppm. TLV from different sources are as follows:
    UK EU OSHA ACGIH
    STEL 35ppm 50ppm PEL 50ppm 35ppm
    LTEL 25ppm 20ppm - 25ppm
    Lethal Concentration 0.5%v/v - - -
  2. Ammonia will taint any food that is stored in cold stores or chillers causing loss of product. This is now less likely with modern systems as the Ammonia plant is isolated from the food area and Glycol or liquid CO2 is used as the coolant in the store itself. However, if the Ammonia can reach the food areas, low level of Ammonia detection is essential to prevent the large financial losses that can ensue from a leak no matter how small.
  3. The plant room is always subject to small leaks due to moving equipment, valves and joints, so a background of Ammonia can be expected. Therefore, the detectors used in these areas should be capable of working in a constant background and the controller should be capable of controlling the ventilation. The detectors here will be capable of reading much higher ranges than the TLV as high concentrations are a real possibility in this application. These plant rooms can vary from a small room requiring 1-4 points to a very large area with many points required.
  4. As Ammonia is flammable albeit difficult to set alight and only at high concentrations (15.4% v/v), it should still be monitored for explosion risk in any area where these levels could be possible. This risk should always be considered where large quantities of Ammonia are stored or compressed. The alarm point is generally set at 1%v/v at which point non-essential electrical systems are shut down.
  5. A typical ammonia absorption system

Solution

The GMI have a wide range of products specifically designed to meet and exceed all the requirements of the refrigeration industry. These systems have been designed to meet the vast range of different applications that are presented by using Ammonia as a refrigerant gas. The Active-8 and Active-80 range of controllers can be fitted with various types of Ammonia sensors dependent on range of detection required. These systems can also accommodate other sensors if required (CO2, Freons, Flammable Gases etc). In addition to these discreet sensor systems, GMI have a range of sampling systems that have been designed to meet the unique challenges of refrigerant applications including Ammonia. However, similar to the Active-8 / 80 range, these can also be fitted with other sensors for other gases that may be of interest. The larger of these systems (Seafarer) is capable of handling up to four gas sensors (Flammable, PPM Ammonia, Freons, CO2 depending on application). This system is capable of drawing samples from up to 32 points and by using a fast flow manifold thus cycle times are kept to a minimum.

Refrigeration

Please note that although Ammonia is lighter than air and should rise to the ceiling in any facility, this will only occur if the gas is at the same temperature as the surrounding atmosphere. With refrigeration gas this may not be true, so gas temperature at a leak point should be considered.