This paper has its origin in a real solvent storage facility with a set of forty-two tanks that require blanketing. The main goal of the study was to optimize the design of the blanketing system, taking into account economical, security and environmental issues, in order to reduce risk related to operating with flammable products and to diminish volatile organic compounds emissions allowing vapour recovery at minimum cost. The proposed design allows significant savings when compared to the design resulting from a traditional approach, both in investment costs (about a twenty percent in the presented industrial case) and in operational costs (the average blanketing gas consumption can be reduced to about a thirty percent).
The main characteristics of this facility are that tanks are located in three adjoining areas, they have the same pressure limits, product vapours are not incompatible and nitrogen is available in the plant. Legislation and technological constraints are also considered. These properties and constraints make possible to pose the possibility of installing a common manifold.
Several configurations of the blanketing system have been analysed taking into account the desirable features of the facility. These configurations have been modelled through the adjustment of an existing software tool for the analysis of piping systems, whose proper operation in this type of problems has been previously validated. The behaviour of the different possibilities has been thoroughly analyzed through the simulation of different probable scenarios by the measure of pressure in vapour space of the tanks.
After optimization, the proposed solution consists of only one manifold joining the vapour spaces of two different groups of tanks. Although this could avoid proper control of pressure in the different tanks, it has been proved that its installation does not affect negatively to the security of the facilities, through simulations of worst case scenarios, Hazop analysis and fault tree analysis.
The final layout entails important improvements with regard to the traditional one which involves each tank being isolated from others and having its own blanketing valves. In the current solution, total length of pipelines and the number of pressure regulating devices is reduced. At the same time, since a range of pressures is allowed in the vapour space, nitrogen consumption is also reduced. These facts lead to simultaneous installation, operation and maintenance costs savings, as well as to a significant reduction in the overall volatile organic compounds emissions to the atmosphere, all of them compatible with improvements in the system reliability.