Apr-2007

Gasification technologies for hydrogen manufacturing

Gasification technology can follow on from upgrading and treating technologies to convert a wide range of heavy residues into syngas, which can be used as clean fuel for high-efficiency IGCC power generation or to produce H2 and/or CO

Joachim Wolff
Shell Global Solutions International BV

Article Summary

Increasingly stringent legislation in all markets has put refiners under greater pressure to improve product quality while raising environmental performance. The Clean Fuel Act in the US, the Auto Oil Programme in Europe and numerous similar legislation efforts as a part of the new definition of automotive fuel quality around the world, including India, are causing drastic limitations for sulphur and aromatics. These two parameters will change the internal H2 balance of refineries because of their counter-current effect. The deep desulphurisation of various fuel streams requires more H2, and the reduction of aromatics will lead to less H2 surplus from catalytic reforming due to low- severity operating conditions.

In such a situation, catalytic reforming as the major source for H2 in refineries will no longer be sufficient to satisfy the growing demand for H2. Consequently, two options for H2 production are becoming more important: steam reforming and partial oxidation. Steam reforming of light hydrocarbons, natural gas or LPG is used to produce the bulk of H2 today. However, partial oxidation of residues (or even petroleum coke) is also being considered.

The disadvantage of the relatively higher investment for a gasification unit compared to steam reforming is mitigated by several factors that will be discussed. One of those is the search for the best techno-economical way to dispose of refinery residues.

In this situation, gasification offers a very versatile process for the conversion of even the heaviest bottom-of-the- barrel refinery residues into clean synthesis gas, which can be used to produce H2, power, fuel gas or steam for various refinery purposes, as well as gases for the chemical industries.

Gasification technology may be able to help facilities rise to these challenges. For example, by producing H2 and power economically.

Residue byproduct disposal challenges
Traditionally, crude-oil residues have been sold as marine bunker fuel or used on-site as furnace fuel. However, refineries are under pressure to reduce both their emissions and the sulphur content of their products, and the market for high-sulphur heavy fuel oils is shrinking. A refinery’s ability to develop an economically effective strategy for disposing of its residue and increasing the yield of lighter, high-value products that meet current and future specifications is paramount.

In response, refiners are cutting deeper into the barrel to maximise their distillate yield. They can do this through different conversion schemes; for example, through residue hydroconversion or deep thermal conversion, followed by deep flashing or solvent deasphalting. However, one byproduct of these processes is a viscous residue of high ash and sulphur. As the market for heavy fuel oil is shrinking, the economically effective disposal of this residue can be a burden. A similar situation occurs when deep conversion is used with coking technologies, producing a petroleum coke residue.

Meanwhile, as crude oil prices continue to raise, many refiners are seeking technological solutions that will enable them to maximise high-value product yields from heavier, sour crude oils rather than paying a premium for light, sweet crude oils.

One solution involves taking an integrated approach. For example, gasification technology can follow on from upgrading and treating technologies to convert a wide range of heavy residues and asphaltenes into synthesis gas (syngas), as shown in Figure 1. This gas can be used as clean fuel for high-efficiency integrated gasification combined-cycle (IGCC) power generation or to produce H2 and/or carbon monoxide (CO). The use of hydrodesulphurisation in refineries to remove sulphur from diesel and gasoline products has led to a sharp increase in H2 demand in recent years.

Over 30 syngas projects involving more than 100 Shell gasification units have been developed or are at the planning stage, two of which will be discussed in further detail.

The special situation in the Indian refining industry has to be considered, where natural gas resources are limited and a significant part of this is dedicated to the fertiliser industry. Therefore, a number of Indian refineries are considering gasification projects for IGCC, for H2 production or in combination for H2 and power.

Indian companies have experience with oil and coal gasification that date backs to the 1960s. Oil gasification offers a technology proven under Indian conditions to provide a reliable source of synthesis gas in industrial service. Over 80% of Indian plants apply the proprietary Shell gasification process (SGP).

Although coal gasification has a good track record around the world, it has played a minor role in India (to date) compared to oil gasification. This situation is based on the particular characteristics of Indian coal — high ash content (up to 45%), with the ash containing high amounts of silica and alumina, resulting in high melting points. Therefore, fluxant addition is less favourable while increasing the ash content further. In comparison, coal beneficiation or blending high-ash coal with pet-coke may prove more favourable.

India has proven reserves of 170 billion tons of coal. When compared with reserves of oil (580 million tons) and gas (540 million tons), coal gasification will need to be regarded as a future resource for India. Since most Indian coal has a low sulphur content (approximately 1%), relatively simple flue gas desulphurisation units can be added with a low investment cost compared to conventional combustion plants that must meet stringent environmental requirements.