Complete process plants (4): Inorganic acids

Last month we said that the next issue to focus on budget cost estimates for complete process plants would give data on industrial gases. Unfortunately, this has had to be put back for the moment. This month, therefore, we focus on plants for the high-tonnage production of sulphuric (H2SO4), nitric (HNO3) and hydrochloric (HCl) acids.

The precursors of H2SO4 can be any one of:

* elemental sulphur, usually obtained from hydrodesulphurisation refinery operations to give hydrogen sulphide which is then, in turn, oxidised to sulphur;

* hydrogen sulphide extracted from smelter (eg, copper) waste gases;

* gypsum and iron pyrites, both of which are not particularly common processes these days.

Because H2SO4 is so widely employed in the chemical and other industries (indeed, it used to be said to be the one commodity whose consumption was the barometer of the economy of the whole nation), we additionally give the plant cost information for the production of sulphur from hydrogen sulphide. The effect of the different feedstocks, sulphur and gypsum, are also illustrated. Finally, by way of contrast, the capital costs for hydrofluoric acid are shown. Per tonne of production, these are much higher than the other products since the technology and materials of construction are markedly different.

Once again, the costs for complete process plants presented here are for budget purposes only and are at a base date of January 1996. The six correlations are given in Table 4, with cost expressed in £million and capacity in tonne/day. Figure 4 graphs these.

Naturally, it is assumed that the plants are built on an established site - their products are mostly required for local use - so that all services (steam, cooling, water, power, air and so on) are available. However, site clearance is excluded.

All of the data in Table 4 and Figure 4 were reasonably consistent with good fit for all of equations 4a to 4f.

{{Table 4: Key and correlations to Figure 4

Curve Process and main Correlation Equationnumber feedstock number

1 Sulphur from hydrogen sulphide Cost = 0.243(Capacity)0.69 4a 2 Sulphuric acid from sulphur Cost = 0.267(Capacity)0.54 4b 3 Sulphuric acid from gypsum Cost = 0.216(Capacity)0.65 4c 4 Nitric acid from ammonia Cost = 0.236(Capacity)0.61 4d 5 Hydrochloric acid from salt Cost = 0.126(Capacity)0.66 4e (sodium chloride) and sulphuric acid 6 Hydrofluoric acid from Cost = 0.665(Capacity)0.78 4f calcium fluoride and sulphuric acid

Note: Cost in £million (Jan 1996) and capacity in tonne/day}}