Following a decision to increase capacity at one of the largest refining/petrochemical complexes in China, SINOPEC commissioned Process Integration Limited (PIL) to collaborate with its engineering subsidiary, Luoyang Petrochemical Engineering Corporation (LPEC), to optimise onsite hydrogen supply and consumption.
The expansion required the installation of additional fluid catalytic crackers, crude oil distillation units and hydrocrackers, all associated with hydrogen-intensive processes. In order to minimise necessary new investment and post-expansion operating costs, a detailed analysis of existing and prospective new hydrogen capacity was necessary. PIL’s state-of-the art software tool, H2-int, specifically designed to enable effective hydrogen network analysis and optimisation, was key to developing a robust set of revamping and optimisation options for the client’s existing hydrogen supply system.
Figure 1.a depicts a typical hydrogen network consisting of major hydrogen consumers and producers within a refinery complex. Using a graphical approach, H2-int initially employs pinch analysis (see Figure 1.b) to target hydrogen supply and demand. This aids in identifying a number of low-risk candidate paths to minimising overall hydrogen consumption within the network. In a secondary step, these candidate paths are then subjected to rigorous mathematical analysis (employing PIL proprietary algorithms) in order to generate an optimum for each selected path.
Importantly, PIL’s H2-int software also takes account of a number of important real-world practical constraints. The net result is a sophisticated yet efficient methodology that can quickly identify significant cost savings that are not just theoretical in nature.
The software provides a highly automated means of generating an optimal yet also affordable hydrogen distribution network design, taking into account many different potential hydrogen sources. Uniquely, H2-int takes into account the varying levels of gas impurity found at different stages of the hydrogen network (via detailed physical property calculations applied to hydrogen consumer/producer units), and can also readily assist in selecting appropriate types and sizes of hydrogen purification unit, indicating where they should be placed within the system as it does so.
Figure 1.a Typical hydrogen network in a refinery complex
Figure 1.b Hydrogen surplus diagram
Maximising available hydrogen supply
The type and capacity of a hydrogen purification unit at a given site has an important impact on the overall utilisation efficiency of the hydrogen network. Working with LPEC, PIL investigated in detail the effects of (i.) installing additional hydrogen purification units at SINOPEC’s site and (ii.) the effects of increasing the capacity of these units. Three different scenarios, summarised in Table 1, were simulated.
Table 1 Hydrogen supply scenarios simulated at SINOPEC refinery/petrochemical site
|Base Case||One membrane unit onsite|
|Case 1||Two hydrogen purification units: one existing membrane unit and one additional PSA unit|
|Case 2||One larger PSA unit (eliminating the existing onsite membrane unit)|
PIL identified that significant but largely similar reductions to the overall hydrogen deficit would be possible in both the ‘Case 1’ and ‘Case 2’ scenario (see Figure 2.a). The operational cost savings in either scenario were also broadly similar (see Figure 2.b). In the event, given that the results indicated only a slight incremental advantage to adopting ‘Case 2’, and since ‘Case 2’ would also incur significantly higher capital expenditure ($7 million/year for ‘Case 2’ vs. $4.9 million/year for ‘Case 1’), ‘Case 1’ was ultimately selected as the preferred option for SINOPEC.
PIL’s innovative approach to analysing the hydrogen network at SINOPEC’s site resulted in a detailed optimisation plan aimed at revamping and restructuring the hydrogen network. Subsequently enacted by the client, hydrogen recovery at the site is now significantly improved on pre-study operations: the flow of fuel gas and the concentration of hydrogen in the fuel gas are both down considerably, which in turn means that the loss of hydrogen from the network has been greatly reduced. Additional extra hydrogen capacity added since the expansion has been kept to a minimum.
Figure 2.a Comparison of total hydrogen deficit
Figure 2.b Comparison of operating costs
PIL has extensive experience of defining and implementing effective refinery hydrogen management strategies at a number of sites worldwide – drawing on more than 30 years of experience and numerous collaborative projects with industry. Beyond its hydrogen expertise, PIL offers a wide variety of software products and consultancy services to the process industries.