Apr-2012

Hydrogen management

Refiners are facing the challenge of meeting increasingly higher quality product specifications to make clean fuels product, while at the same time purchasing lower-quality 
H2-deficient crudes.

KBC Advanced Technologies

Article Summary

As a result, H2 requirements have been steadily increasing and refineries are finding that proper H2 management is increasingly important to their long-term viability. This article will describe the process KBC has successfully used to eliminate H2 availability constraints and prioritise H2 use in order to improve profitability.

Increasing refinery complexity and H2 requirements
Refineries have various levels of complexities and operating objectives. The simplest refinery type is the hydroskimming refinery. Figure 1 show a typical hydroskimming refinery configuration. Hydroskimming refineries typically do not need a H2 plant, as the H2 demand can be adequately met by the naphtha reformer. Margins are often low at hydroskimming refineries unless there is a large marketing advantage, usually based on location.

It is typically advantageous to maximise the production of higher-value transportation fuels instead of lower-value fuel oil products. As a result, most profitable refineries are either moderately complex or highly complex facilities that have cracking and conversion units. H2 requirements can vary greatly from one configuration to the next.

Figure 2 shows a typical configuration for a moderately complex refinery, which employs an FCC and a visbreaking unit to increase product value. The addition of a gas oil hydrotreater for the FCC feed increases the refinery H2 demand beyond what the reformer alone can provide. A small  H2 plant is therefore also needed.

Figure 3 shows a complex carbon rejection refinery. A coker is added to convert fuel oil to more valuable products. Light coker gas oil is hydrotreated in the diesel hydrotreater and heavy coker gas oil is hydrotreated in the gas oil hydrotreater. Now, a medium-sized  H2 plant is required.

Figure 4 shows a complex hydrocracking refinery configuration. Substituting a hydrocracker for the FCC unit increases H2 requirements to the point where a large H2 plant is required.

Finally, Figure 5 shows that the addition of residua hydrocracking to reduce the size of the coking unit and the amount of coke produced requires a very large H2 plant.

The most complex refineries generally have the highest incremental value for H2. These refineries can benefit the most from a  H2 management study when H2 availability becomes a refinery limit.

H2 management study methodology
Like most successful refinery studies, H2 management is a concept that starts with the unit review and ends with implementation of the results in the field. The goal is to improve the use of H2 at the refinery and improve the profitability of the refinery.

During the identification phase, the H2 system is reviewed to identify areas for opportunity by improving the utilisation of H2 at the refinery. In the evaluation phase, the identified opportunities are then further studied using individual or combined tools to determine the value to the refinery and the implementation cost. The implementation phase is the final piece of the study. In this phase, the identified solutions are put into place at the process units in order to achieve improved refinery profitability. All three phases of the project are necessary to have a successful project.

H2 management study goals
The goal of a H2 management study is to develop a thorough understanding of the refinery H2 system. The process begins by building a complete H2 system flow diagram and developing a reconciled balance of the entire refinery H2 system. Orifice flow meters are notoriously inaccurate in measuring H2 flow, primarily because of the significant variations of MW that can occur in H2 rich streams. In addition to meter corrections, a basic understanding of the typical range of chemical H2 consumption and solubility/purge losses for each H2 consumer is often essential to closing the H2 balance properly.

Once a balance is developed, it is important to determine the value of incremental H2 at each consumer and the cost of producing H2 at each H2 source. A complex refinery can have many distinct H2 subsystems segregated by geography, H2 purity and/or pressure. The incremental cost and value of H2 at each system is likely different, and some H2 subsystems may be highly 
vulnerable to upsets that could be mitigated if connections between isolated systems are established.

The primary goal of a H2 management study is to identify the constraints imposed by the overall system and various H2 subsystems, and find ways to remove these constraints to improve overall refinery profitability. Typical solutions can be as simple as rerouting streams to maximise high-margin units at the expense of others or more complex and capital intensive, such as building H2 recovery units, debottlenecking steam-methane reformers or installing additional compression to provide additional flexibility and increase profits.

H2 management study tools
Refinery H2 systems can be extremely complex. As a result, it may be very difficult to evaluate all of the possible H2 management opportunities without the aid of specialised tools. KBC has developed two software products that are used in our H2 management studies. The combination of KBC’s  HydrogenPinch and Petro-SIM software is extremely effective in evaluating the value of rerouting streams and/or removing constraints in order to improve overall refinery profitability.

HydrogenPinch is KBC’s proprietary software designed primarily to identify H2 system opportunities such as the optimal routing of H2 streams at a refinery. This software evaluates the  H2 pressure, purity and flow of each supplier and consumer in the refinery using a pinch method that is analogous to the Energy Pinch concept, which revolutionised energy conservation a few decades ago.