Retrofitting Foaming Plants to Use

The knowledge that the use of blowing agents such as CFCs or HCFCs contributes to the destruction of the ozone layer and global warming

The knowledge that the use of blowing agents such as CFCs or HCFCs contributes to the destruction of the ozone layer and global warming, triggered changes in environ- mental legislation.

The resulting bans on certain products and production methods prompted the development of new technologies. For the polyurethane industry this means that new blowing agents have to be used. Today, in the area of rigid or insulation foams, pentane is in widespread use as an environmentally compatible blowing agent.

The main applications of pentane as a blowing agent are in:

• the refrigerated appliance industry,
• foaming lagging around piping systems,
• the manufacture of metal compounds and insulating panels.

Processors using pentane or pentane-containing polyurethane raw materials must take into account the potential hazard of explosive atmospheres being created. The explosion risk applies to the entire processing line, from the pentane storage area to the cured polyurethane foam

•  Information required for a successful retrofit

• To ensure a plant retrofit is effective, the plant-operating company should provide the following information:

A) Product information

- Dimensions of the end products

- Component weight

- Quantities/production volume

- Material consumption

B) Data on the foam system

- Amount of blowing agent in relation to polyol

- Polyol/isocyanate mixing ratio

- Raw polyol viscosity

- Isocyanate viscosity

- Blowing agent: C-pentane, N-pentane, I-pentane

C) Information on the place of installation

- Machine layout

- Floor plan

- Ambient conditions (temperature, height above sea level)

- Adjacent workplaces with potential ignition sources (e.g. welding or soldering)

- Raw material supply

- Form in which polyol, isocyanate and pentane are supplied (typically: drums, containers, tank vehicles)

D) Information on the existing plant or machine

- Machine type (wet-end), high-pressure or low-pressure

- Age, manufacturer,  type

- Type of plant or machine control system

- Number of foaming places

- Description of the dry ends, plant components

- Description of foam filling (closed or open output)

- Type of mixhead guidance (manual guiding, robot, portal)

- Mould material (hazards due to static electricity)

• Pentane safety concept

The safe operation of a production system requires a consistent and comprehensive safety solution to be implemented right from the planning stage. We developed its Pentane Process Technology (PPT) to address this need. The PPT system is a graded and interlinked safety process comprising  a combination of primary and secondary measures. All primary measures are aimed at one common, important goal: they pre- vent the formation of potentially explosive atmospheres at the outset. These measures cover the entire processing line, from the tank storage facility to the foaming station. This includes special fittings for the component lines, automatic switch-off devices, shut-off valves and nitrogen inerting equipment. Additional system and operational safety is provided by secondary measures such as:

• enclosures,
• special ventilation and exhaust systems,
• gas alarm systems with appropriate sensors,
• pentane extraction equipment,
• leakage monitoring and fault indicators,
• defined plant disables.

• Retrofitting measures required:

Pentane is usually stored outside the factory building in underground or aboveground tanks. The design is similar to that of storage tanks at petrol stations.

The following basic equipment must be provided:

Suitable hoses for liquid unloading and vapour return must be available and compatible with existing connections. Conductive hoses are required. Short liquid hose will minimise spillage after unloading has finished.

It is recommended that the tank level indicator should be readable at the unloading spot.

To be installed.

To be installed.

e) Emergency telephone

To be positioned nearby.

f )   Safety control system

Unloading area to be included in the safety control system.

The different characteristics of underground or aboveground tanks are listed below:

• Aboveground tank:
  • Easy inspection
  • Single-wall tank sufficient
  • More protection required against fire, sun, weather
  • Larger temperature variations – emission losses

• Underground tank:
  • Less protection required against fire, sun, weather
  • Lower max. temperature
  • Gravity sufficient for unloading truck
  • Inspection difficult
  • Double-wall tank with leak detection system needed

Instead of using tank storage facilities, the system can also be supplied from 1,000l containers or drums.

The selected design has to comply with national legislative requirements for the storage of substances that are easily flammable and detrimental to groundwater. Total explosion protection according to zone and alarm plans and integration into an approved safety concept must be ensured.

B) Polyol/pentane premixing station

At present, a commercial-scale supply of pre-mixed polyols is not available. In general, operators therefore have to prepare the mixture on site.

• Primary safety measures for pre-mixing polyol:
  • use of a double-shaft seal including safety sealing liquid system;
  • pentane lines are equipped with two-ferrule tube fittings;
  • polyol-pentane mix lines are equipped with two-edge cutting ring fittings;
  • pipelines are equipped with two-edge fittings;
  • safety sensors;
  • use of pressure switch and safety valve technology.

As a secondary safety measure, integration into the extraction system and gas alarm system is necessary.

C) PUR high-pressure foaming machine, two components

A high-pressure foaming machine is used for metering the mixture and blending polyol/pentane with isocyanate.

A basic requirement  for the safe operation  of the high-pressure metering machine is to prevent the formation of hazardous pentane/air-mixtures, i.e. the air-tightness of the system has to be ensured. For example, all dynamic seals are double and fitted with liquid safety sealing systems.

The different shot weight requirements for cabinets and doors are solved by putting in place a frequency converter for the high-pressure foaming machine’s metering pumps.

The safety sealing system is a small container that is connected to the sealing gap. The container is filled with a sealing liquid and closed with a diaphragm. If a leak occurs, the level change in the tank is detected by a sensor and transmitted to the safety control system.

• To avoid the formation of an explosive atmosphere,  the following primary measures must be put in place for the polyol/pentane tank:
  • the tank inside must be inerted with nitrogen;
  • the stirrer shaft must be equipped with a double-shaft seal and safety sealing liquid system;
  • double-sealing screw fittings;
  • protection against overpressure;
  • self-closing valves for filling and emptying;
  • pentane-specific level metering and refill control;
  • adjustable valve for nitrogen venting

In addition, the work tank comes with automatic overfill protection and a permanently active level sensor that is integrated into the pentane safety control system.

• Additional measures:
  • Integration of the work tank into the extraction system
  • Integration into the gas alarm system
  • Integration into the PPT safety control system
• Further primary safety measures are:
  • Rigid pipe between machine and day tank
  • Twin-type seal for drive shaft and hand wheel shaft/adjustment rod
  • Closed venting system of the relevant analyses sections
  • Closed filter
  • Screw connections with double sealing function
  • Mix heads with leakage monitoring
  • Ring main closing valve with leakage monitoring
  • Min./max. pressure monitoring
  • Splash protection if required

 D) Pentane-relevant dry-end retrofits

• The dry part of a refrigerated appliance production line comprises supporting fixtures for the production of cabinets and stationary or mobile molds for door production. Required safety measures:
  • The area around the foam filling location requires a design that complies with the
• ATEX directive and implementation of the explosion and alarm zone plan.
  • During the foam filling process, electrical loads such as the mold temperature control system must be disconnected.
  • Integration of the plant into the equipotential bonding system.
  • Integration into the gas warning system.
  • Integration of the supporting fixtures or the door molds into the extraction system. The extractors should be designed so that they capture the pentane gas right at the point of emission. The extraction system is controlled centrally by the PPT safety control systems.