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Guidelines for Air Emission Regulation 7. Design and operation of tanks and silos7.1 IntroductionTanks are normally used to store liquid substances, whereas silos are used to store solid substances. For the purposes of these Guidelines, "Very noxious substances" means substances that are present in the gaseous phase in concentrations corresponding to more than 100,000 LE/m3 at the storage temperature. Tanks to be used for gaseous substances are not included. There is no need to carry out OML calculations for tanks and silos. 7.2 Tanks7.2.1 Storage tanks for principal group 1 substances and very noxious substances70The exterior walls and roofs of tanks situated above ground should be painted in a colour with a total reflection coefficient for radiant heat of at least 70 per cent. For existing tanks, this can be carried out as part of standard regular maintenance work. This requirement regarding paint does not, however, apply to tanks linked to a condensation plant or other air-cleaning plants. 7.2.1.2 Existing tanks with external floating roofs Tanks with external floating roofs and intended for storage of principal group 1 substances and very noxious substances should be fitted with a primary seal, covering the ring-shaped gap between the tank walls and the outer circumference of the floating roof. They should also be fitted with a secondary seal above the primary seal. These seals should be designed so that at least 95 per cent of the vapours are retained when compared to corresponding tanks with fixed roofs which are not fitted with equipment designed to retain vapours (i.e. tanks with fixed roofs, fitted with a pressure/vacuum safety valve only). All new tanks should be constructed either as tanks with fixed roofs linked to a condensation plant (air-cleaning plant) or designed with an external or internal floating vapour barrier with a primary and secondary seal that meets the requirements stipulated in section 7.1.1.2. 7.2.1.4 Existing tanks with fixed roofs Existing tanks with fixed roofs should either be linked to a condensation plant in accordance with the provisions laid down in Appendix 3 of Statutory Order No. 852 of 11 November 1995, or be fitted with an internal floating vapour barrier with a primary seal, constructed in a way that a total of at least 90 per cent of the vapours are retained when compared with corresponding tanks with fixed roofs and not fitted with equipment designed to retain vapours. Tanks should be filled by injecting liquid below the surface level inside the tank. Example of storage in a closed system
7.2.2 Storage tanks for principal group 2 substances, including diesel oil and other substances not mentioned under 7.1.1The guidelines specified below apply to tanks larger than 50 m3. Products with a vapour pressure greater than 1.3 kPa71 should be stored in tanks with fixed roofs. These tanks should be linked to a condensation plant in accordance with the provisions laid down in Appendix 3 of the Statutory Order on the limitation of emissions of vapours from storage and distribution of petrol. They may also, however, be fitted with an internal float with a primary seal, which should be constructed in a way that a total of at least 90 per cent of the vapours are retained when compared to corresponding tanks with fixed roofs and not fitted with equipment designed to retain vapours. Products with vapour pressures less than 1.3 kPa (diesel oil, heavy fuel oil, and other substances with similar vapour pressures) should be stored in tanks with fixed roofs and a pressure/vacuum valve. Pressure/vacuum valves may be omitted on existing tanks not constructed for varying pressures corresponding to the range of the pressure/vacuum valve. The exterior walls and roofs of tanks situated above ground level should be painted in a colour with a total reflection coefficient for radiant heat of at least 70 per cent. For existing tanks, this can be carried out as part of standard regular maintenance work. Tanks should be filled by injecting all liquids below the surface level within the tank. 7.3 SilosSilos for storage of solid substances should be fitted with suitable filters (V-pocket filters or filter cartridges), so that the limit values for emissions set up in these Guidelines for Air Emission Regulation can be complied with in connection with filling the silo. Example of air terms for a silo filter
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