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Methods of vapour control One solution lies in applying vapour recovery followed by vapour destruction to thermally oxidise the VOCs not recovered in the fi rst step (consisting mainly of methane and ethane). Firstly, the vapour recovery unit (VRU) will recover the C3+ hydrocarbons, after which the vapour combustion unit (VCU) will oxidise (combust) the C3- hydrocarbons not recovered by the VRU. The combustion of the exhaust vapours occurs in a safe and temperature-controlled process under an enclosed stack (Figure 2); the system is equipped with safety and control devices to cover the operational range set by the design basis. But the thermal oxidisation of H 2 S emits harmful sulfur oxides (SO X ), which are major air pollutants that contribute to acid rains. SO X emissions are regulated by law in most countries and with the concentration of H 2 S typically found in the majority of crude vapours, these regulations prevent it from being discharged into the atmosphere. Therefore, it must be eliminated prior to combustion. The traditional method of removing H 2 S in refi neries or chemical plants is amine or sodium hydroxide (NaOH) solution scrubbing. These processes are costly, complex, require utilities (e.g. steam, waste water treatment) and are mainly applicable in continuous and steady state operations. These conditions are not typically found in the storage and distribution industry. An effective and simple solution for H 2 S removal is the use of sacrifi cial guard beds fi lled with special activated carbon, as illustrated by the following formulae: Carbon impregnated with potassium hydroxide (KOH), in the presence of oxygen and for low H 2 S concentration (up to 30 ppm): H 2 S + 2(KOH) Æ K 2 S + 2(H 2 O) Carbon impregnated with potassium iodide (KI); also effective with stoichiometric presence of oxygen and with higher H 2 S concentration (up to 1000 ppm) in the vapours: 2(H 2 S) + O 2 Æ 2S + 2(H 2 O) Figure 3. AEREON vapour control system (two VRUs and one VCU) installed in the Far East. $OOLQRQH BUCHEN-ICS GmbH Emdener Str. 278 // 50735 Cologne // Germany info.ics@buchen.net // buchen-ics.com A company of the REMONDIS Group WDQNFOHDQLQJ 6LORFOHDQLQJ &KHPLFDOFOHDQLQJ &DWDO\VWKDQGOLQJ 5HDFWRUVHUYLFHV $XWRPDWHG

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