West revamps eastern ammonia

Source: ECN


Recession has initiated innovations in plant revamping. As the poorer nations of the east cry out for this technology, western nations line up to provide it. Susan Royse surveys what is on offer and why ammonia plants offer more scope for revamping.

AS THE purse strings tighten worldwide, revamping, or modernising, existing plant is becoming an increasingly attractive alternative to scrap and rebuild. A revamp can provide what is effectively a new plant with operating costs, reliability and ease of operation to match, at a fraction of the cost.

Nowhere is the approach more relevant today than in the cash-starved former Soviet Union and Eastern Bloc countries. The outdated and inefficient plant that sufficed in the cushioned communist world of state subsidies and guaranteed markets will not survive in the cut-throat capitalist world to which these countries are now exposed.

Western European contractors, technology licensors and catalyst suppliers are lining up to present cost-effective revamp solutions to the former state run industries, in particular to the. fertiliser industries. Westerners such as H&G Process Contracting, ICI, Uhde and Ammonia Casale are competing with the former Eastern Bloc's own industrial research and development centres such as the State Nitrogen Industry Institute of Moscow (GIAP) and the Fertilizers Research Institute of Pulawy.

'The greatest scope for applying technical innovations within a fertiliser complex is on the ammonia plant,' Trevor Nurse of H&G told delegates at a conference* on revamping held recently in Budapest. A range of improvements may be considered (see below), relating to the process operations in the ammonia plant (desulphurisation and reforming), the process air compression, gas purification, synthesis gas compression and the ammonia synthesis.

Separate process units can be constructed to supplement, or ultimately replace, existing units. This can be the basis of a stage-wise modernisation and replacement at an economic cost and without incurring any energy penalties compared with latest plant designs, Ian Barton of ICI Katalco suggested.

In this respect, ICI is now actively promoting its LCA (Leading Concept Ammonia) technology, which aptly decouples the individual process steps and eliminates the need for energy integration to achieve overall efficiency. The LCA process has been demonstrated in two grassroots units at ICI's Severnside site in the UK since 1988.

More than any other aspect, catalyst upgrading probably holds the key to the successful revamping of ammonia plants. The latest generation of catalysts can bring about significant improvements in reliability, yield and efficiency, at low risk and with short payback periods.

Barton highlighted four specific areas which ICI has addressed. The first is inclusion of a pre-reformer, made possible by the development of a high activity nickel catalyst which can promote reforming reactions at low temperatures, Barton explained.

For an existing ammonia plant, the arrangement offers the advantages of reduced fuel usage in the reformer, increased radiant efficiency in the reformer due to a lower heat load, the potential to increase plant throughput, increased feedstock flexibility and a lower steam-to-carbon ratio.

The second catalyst development that has affected the design and operation of ammonia plants, according to Barton, is the shaped reforming catalyst, offering increased activity and heat transfer over the basic ring shape of the traditional catalyst. ICI Katalco's four-hole catalyst (essentially a cylinder with four small longitudinal holes through it with a relatively high length to diameter ratio) has been used to reduce significantly the size and cost of new reformers, he claimed.

Other developments include a modified high temperature shift catalyst, offering a more flexible choice of steam ratios and longer life, and new low temperature shift catalysts for maximum resistance to poisons and low temperature activity. 'These four catalyst developments can combine to improve plant output by 10-15%, while also extending the time between catalyst change-outs,' Barton concluded.

H&G has recently completed a feasibility study, cost estimates and basic design for modernising four Chemico-designed ammonia units at Togliattiazot, Russia. The project, to increase the capacity of each unit from 1350 tonne/day to 1500 tonne/day, is proceeding in stages. Replacement of the reactor internals by an Ammonia Casale design incorporating two heat exchangers and addition of an ammonia wash vessel for the makeup gas to ammonia loop are included in the first stage, Nurse explained.

Other recommendations made by H&G include addition of a mechanical steam compressor to the existing Benfield regenerator, a reduction in the steam-to-carbon ratio, rearrangement of the ammonia loop piping to reduce the refrigeration load, installation of a new distributed control system and replacement of the internals of the synthesis gas compressor.

H&G has similarly carried out plant audits and cost estimates to modernise five synthesis gas production units and six ammonia synthesis units operated by Chimco of Vratza. The Bulgarian company is looking to increase the ammonia output from 1500 tonne/day to 1800 tonne/day. Engineering and procurement activities have begun to replace the lining of the primary reformers and convection section with ceramic fibre and to install a natural gas saturation unit, a new distributed control system, a new shutdown system and a new uninterruptible power supply system.

Another Bulgarian plant urgently in need of modernisation is the nitrogen complex of Agropolychim at Devnya. Like many plants in the former Eastern Bloc, it has a number of points in its favour: it is situated close to a port connected to the Black Sea, on a pipeline bringing natural gas from Russia and has a good local supply of skilled labour.

But, addressing the conference, a company representative conceded that to stay in business the capacity of the ammonia plant would have to be increased by 50% and at the same time its energy consumption reduced to under 8 Gcal/tonne of ammonia.

'We also have plans to build a urea plant with a capacity of 200 000 tonne/year and a UAN solutions plant and, because the existing installation fails to meet technical and economic requirements, to replace the ammonium nitrate plant with a new one,' he said.

Agropolychim is seeking finance for the project, estimated to cost $110m. 'Our shortage of funds requires a grace period of three years and a barter arrangement for payment in product. An alternative to this arrangement could be a joint venture, stimulated by the new liberal changes in Bulgarian legislation governing foreign investments,' the representative added.

The market for revamping is by no means restricted to eastern Europe. Continued operation of older, less efficient plants has become increasingly uneconomic worldwide in current times of low ammonia and fertiliser prices.

A senior representative of the Indonesian company PT Pupuk Kalimantan Timur (Kaltim) outlined a current revamp of the unique Kaltim I complex, built in 1974. Original over-ambitious plans called for the plant to be constructed on two large self-propelled ships, which would be moved periodically from one offshore gas well to another as supplies became depleted.

A more down-to-earth rethink led to the plant being sited on land, at Bontang in the province of East Kilimantan, but the complicated utility system devised for the ship-borne concept was retained. Despite modifications in 1979 and again in 1984, the plant remains difficult to operate and maintain. Gas consumption is about 30% higher than for a typical plant of the same capacity designed in 1989.

Kaltim, with assistance from the Japanese contractor Chiyoda, is looking to improve the performance of the plant by increasing production capacity by approximately 20%, while simultaneously reducing energy consumption by 10% and improving reliability. The current revamp project is designed to increase ammonia capacity from 1600 tonne/day to 1800 tonne/day and urea capacity from 1700 tonne/day to 2125 tonne/day, while reducing the energy requirement per tonne of ammonia from 42.47m to 38.44m Btu. Expected energy savings per tonne of urea amount to 220 kg of steam and 25 kWh of electricity.

Another key Asian fertiliser plant successfully revamped is the Asean Bintulu Fertilizer plant located in Sarawak, Malaysia, which started up in 1985. The original plant's capacity was successfully uprated last year from 1000 tonne/day to 1200 tonne/day, Heinz Graeve of Uhde reported. Uhde was responsible for the basic engineering, detailed engineering and procurement, with Indonesian contractor Rekayasa responsible for construction.

The revamp had four main aims: to increase the ammonia production capacity to 1200 tonne/day, to reduce specific natural gas consumption by at least 6%, to keep investment as low as possible and to ensure that the emissions and noise are kept to a minimum in compliance with Malaysian environmental legislation.

Revamping can also be a good proposition for urea. In many cases, the main driving force here is the need to increase production capacity relatively quickly, the level of investment depending on the desired percentage capacity increase. There are two possible approaches, representatives of Stamicarbon suggested.

The first is to aim for the greatest possible capacity increase using the existing high-pressure equipment. This involves only minor modifications and the addition of low-pressure equipment. In most cases the evaporation and/or prilling system will need only slight modification.

The second approach is an extension of the first. Capacity can be increased by a further 20-40% by installing an additional medium-pressure stage receiving extra solution bypassed round the stripper from the reactor. The extra ammonia and carbon dioxide condense in the medium-pressure stage, the heat of reaction being used to evaporate water from the urea solution. Investment in this case is substantially higher, but can still be an attractive possibility, they concluded.

The Swiss company Ammonia Casale, which has been active in ammonia revamping for a number of years, has also recognised the opportunities presented by the move towards urea revamping. The company has recently set up a specially dedicated subsidiary, Urea Casale, to target revamp projects.

In 1991, the company won its first major contract to modernise two large urea units based on the ammonia stripping process at the Togliattiazot complex, Russia. Overall capacity is to be raised from 3000 to 3500 tonne/day. Several other similar projects, for capacity increases of up to 50%, are being negotiated, Lodovico Mariani revealed.

*Revamp - European fertiliser plant retrofitting conference, organised by British Sulphur in Budapest, Hungary, on 9-11 September 1992.

Suggested improvements in the desulphurisation and reforming process

  • Change to a lower temperature zinc oxide catalyst for desulphurisation
  • Change to a more active reforming catalyst with lower pressure drop and higher heat transfer characteristics
  • Install an adiabatic pre-reformer to convert the hydrocarbon feed to a more suitable methane feed for the tubular reformer
  • Reduce the steam-to-carbon ratios
  • Install a reformer feed saturator in which the feed is saturated with water vapour by contact with circulating hot condensate. Process steam is thereby reduced and low grade waste heat can be used to heat the condensate
  • Change the reformer tubes with tubes of higher strength material thereby reducing the tube thickness and increasing the internal tube diameter to provide a larger catalyst volume and higher throughput
  • Replace refractory brick insulation in the primary reformer and convection section with ceramic fibre to reduce heat losses and air in-leakage
  • Install higher efficiency burners with improved combustion characteristics in the primary reformer
  • Bypass some of the reformer feed, with or without process steam, around the primary reformer to the secondary reformer. The amount of process air is increased to provide the additional heat required in the secondary reformer
  • Replace the secondary reformer burner with a longer lasting, more efficient ceramic burner
  • Modify the heat recovery in the convection section to reduce the flue gas temperature at the stack
  • Install modern designed waste heat boilers

Source: H&G Process Contracting

Suggested improvements in purification of the reformed gas

  • Change the high temperature carbon monoxide conversion catalyst to one that operates at lower temperature and steam-to-gas ratio
  • Install an isothermal low temperature carbon monoxide reactor
  • Change the type of CO2 absorption solution, solution additives and column packings
  • Install solution flash stages and return the flashed steam to the CO2 regenerator thereby reducing the external heat requirement for reboil
  • Use a low temperature methanation catalyst
  • Install a pressure swing adsorption unit in parallel with the CO2 absorber to remove excess nitrogen and to adjust the H2-to-N2 rates in the synthesis gas

Source: H&G Process Contracting