High temperature insulation wools

[9, IPC Guidance S2 3.03 1996] [41, ECFIA 1998] [143, ECFIA November 2008]

The main output for high temperature insulation wools production is bulk wool and blankets.

The yield from raw materials to melt is generally greater than 90 % and the yield from melt to finished product (blanket/bulk) ranges from 55 to 95 %. However, it is important to note that the yield from melt to finished product is an estimate and may vary according to the type, nature, volume and duration of the production. In particular, the lowest level corresponds to specific and more technically difficult productions.

3.9.1 Process inputs

High temperature insulation wool includes amorphous alkaline earth silicate glass wool (AES) and aluminium silicate glass wool: refractory ceramic fibres (ASW/RCF). Polycrystalline wools (PCW) are not covered in this document, due to the different chemical processes applied for production. There are two main product formulations for aluminium silicate wools: high purity alumina-silicate and zirconia alumina-silicate and four main product formulations for AES wools: calcium-silicate glass wool, silicate wool, calcium-magnesium-zirconium-silicate wool, magnesium silicate wool, the compositions of which are given in Section 2.10. The main raw materials are given in Table 3.48; they are a combination of natural (usually processed) and synthetic substances.

Table 3.48: Materials utilised in the high temperature insulation wools sector

Description Materials

Raw materials for melting

Oxides of aluminium, calcium, magnesium, silicon and zirconium. Also smaller levels of oxides of potassium, sodium, titanium, iron and chromium utilised in the amorphous high temperature wools sector

Secondary processing

For vacuum forming, a wet colloidal mixture of starch, latex, silica or clay is used.

Other activities may use similar substances and sometimes fillers and organic polymers or resins

Fuels Electricity, natural gas, and sometimes light fuel oils (backup, heating) Water Mains supply and local natural sources (wells, rivers, lakes, etc.) Ancillary

materials

Packaging materials including plastics, paper, cardboard, and wood. Mineral oils (fibre coating and other general uses).

Water treatment chemicals for cooling water and waste water

The raw materials for the melt are blended to give the required compositions on melting. In general, over 90 % of the composition of ASW/RCF is derived from silicon dioxide, aluminium and zirconium. Silicon dioxide is derived mainly from high-grade silica sand; aluminium oxide (alumina) can occur naturally but is usually derived by processing bauxite. Zirconium dioxide occurs naturally as baddeleyite or can be manufactured. Other components such as calcium oxide and magnesium oxide used for AES are derived from raw material such as dolomite and lime.

Waste materials are recycled if possible either directly to the furnace as powders and sometimes into the products as wool. Secondary processing can be very specific. The substances identified in Table 3.48 for vacuum forming are common but others may vary widely.

The main uses of water in the high temperature insulation wool sector are for cooling circuits and cleaning. Cooling water is used, usually in closed circuits, to cool various pieces of equipment with corresponding losses from evaporation and purges. Water is also used in vacuum forming operations and for boards and papers. Actual water consumption and water

vapour emissions may vary according to local conditions (e.g. ambient temperature and the hardness of water input).

The energy source for melting is exclusively electricity but natural gas is often used for downstream activities, particularly drying.

3.9.2 Emissions to air

3.9.2.1 Raw materials

In most modern high temperature insulation wool processes, silos and mixing vessels are fitted with filter systems which reduce dust emissions to below 5 mg/Nm³. Mass emissions from both filtered and unfiltered systems will depend on the number of transfers, and the amount of material handled.

3.9.2.2 Melting

Emissions from melting are generally very low consisting mainly of dust from raw materials used in the batch composition charged to the furnace. The raw materials are usually very pure and consist almost exclusively of oxides; therefore, there is little degassing and no significant emissions of gaseous compounds. Most furnaces are served by an extraction system that vents via a bag filter. Dust emissions are generally below 20 mg/Nm³.

3.9.2.3 Downstream activities

Dust and fibrous dust releases can be generated from a number of areas within the process which include: fiberisation and collection, needling, lubricant burn-off, slitting, trimming, cutting, packaging, and areas of secondary processing. All areas where particulate or fibrous dust releases may be generated are usually served by an efficient extraction system which vents to a fabric filter system. Dust emissions are generally below 20 mg/Nm³ and fibre emissions are in the range of 1 – 5 mg/Nm³. Low levels of organic emissions may also occur from some secondary processing activities, in particular from drying, and the related emission levels are usually less than 50 mg/Nm³.

3.9.2.4 Diffuse/fugitive emissions

The main source of diffuse/fugitive emissions in the high temperature insulation wool sector is related to the cutting, handling and packaging operations.

Storage of lubricants used to soften the wools (polyethylene glycol solution) may represent a minor source of diffuse/fugitive emissions in the case of spillage.

Normally, cutting operations are performed with machines equipped with a vacuum system that conveys fibrous dust to a bag filter.

Packaging and handling operations are carried out by applying a vacuum suction to the cardboard boxes.

The specific issues related to the potential diffuse emissions of fibrous dust are normally managed by health and safety regulations at work and they are controlled according to workplace exposure levels. In particular, exposure to aluminium silicate glass wool (ASW/RCF) is carefully controlled in the workplace, this material being classified as a Category 2 carcinogen (see Commission Directive 2009/2/EC).

3.9.3 Emissions to water

As discussed earlier, the main uses of water in this sector are cleaning, cooling, and for vacuum forming and other secondary processing. The aqueous emissions are limited to the cooling water system purges, cleaning waters and surface water run-off. The cleaning waters do not present any particular issues that would not be common with any industrial facility, i.e. inert solids and oil. Cooling system purges will contain dissolved salts and water treatment chemicals. Surface water quality will depend on the degree of drainage segregation and site cleanliness. Water used for vacuum forming is recycled with a purge, which may contain low levels of organic substances. Simple abatement techniques such as settlement, screening, oil separators, and neutralisation can be found within the sector.

3.9.4 Other wastes

[41, ECFIA 1998] [143, ECFIA November 2008]

Waste levels are generally low in the HTIW sector. Wherever possible, waste materials (batch, edge trims, etc.) are recycled either directly to the furnace (which requires processing for wools) or into the products.

At the end of a furnace campaign (in general, every six months), the refractory structure is dismantled and replaced. The material generated from dismantling can be used in other productions processes after milling into powder (e.g. for brick production and as sandblasting material).

About 95 % of the powdered material and other solid waste are reused.

Waste is also produced in the form of the material collected in the dust abatement equipment. In general, this material is not recycled directly to the furnace. Potential contamination and uncertainty over composition make this difficult but some initiatives are underway to address the issue. Due to the nature of the material, it can be expensive to dispose of and this helps to provide an incentive to finding alternatives, so the tendency to produce waste is decreasing due to the price increase for waste disposal, energy and raw material.

Most mineral raw materials are delivered in bulk (via silo tracks) and do not give rise to packaging waste. Waste materials from product packaging operations (plastic, cardboard, wood, etc.) are usually reused or recycled if practicable. Other waste non-specific to the sector is disposed of by conventional means, or recycled where local or national schemes permit it.

The EU ASW/RCF and AES sector as a whole produces around 700 – 900 tonnes per year of waste which contains fibres, and 100 – 700 tonnes of other waste.

3.9.5 Energy [41, ECFIA 1998]

There is little information available on energy use within the ASW/RCF and AES sector.

Melting is exclusively electrically heated with very low volatile losses. Therefore, the direct melting efficiency (excluding off-site issues) is quite high, although the composition has a high melting energy requirement and the furnaces are relatively small. The energy consumption ranges from 6.5 – 16.5 GJ/tonne of melted product. The energy consumption for the other activities ranges from 3.5 – 9.5 GJ/tonne product (based on 75 % conversion of raw materials to finished product).