When the ship comes in

Previously, a little known operation that was only called upon at times of extremely high gas demand, the Grain LNG facility on the Isle of Grain is now the centre of one of the most ambitious industrial expansion projects in the UK — driven by growing awareness of the potential of LNG (liquefied natural gas) to offset the rapid decline in North Sea gas supplies.

LNG is natural gas, cooled to around -162°C, where it liquefies and occupies about 600 times less space than at standard temperature and pressure. These characteristics enable it to be shipped from remote locations in insulated tanks, then regassified and sold on to end-users in energy-hungry parts of the world.

Situated on the river Medway on the Kent coast — just 30 km east of London — the site operated by Grain LNG, a subsidiary of National Grid, is one of four strategically located LNG terminals being developed in the UK.

The Kent terminal, which was originally commissioned in 1982 as an LNG peak shaving plant, has undergone a phase I development to convert it into an LNG import and regassification terminal. The site went live on 7 July, 2005, with a capacity of 3.3 million tonnes of LNG per year.

At the site, LNG is pumped through cryogenic pipelines into four 50,000m3 storage tanks. When required, the LNG can be regassified by heating and fed into the National Transmission System (NTS) via a pipeline connected to the site, explains Simon Culkin, operations manager at the terminal.

Skanska Ltd led the £130-million phase I project, which involved the construction of a 1km-long jetty and a 4.5-km cryogenic pipeline system, which is rated at 12,000 m3/hr (5,000 tonnes/hr).

The EPC contractor installed new compressors, vaporisers and connections to the four refurbished storage tanks to achieve more efficient and large-scale boil-off gas compression for ship offloading at the site.

Grain LNG is now investing £350 million in a phase II expansion, which will increase the terminal’s capacity to 9.8 million tonnes/year — 12% of the UK’s annual natural gas demand.

Due on-stream in late 2008, the new project features the construction of three tanks of 190,000 m3 capacity. These massive vessels have an outside diameter of 92.4 metres and are over 50m high —large enough to contain the Royal Albert Hall.

Work on phase II started in early 2005 and is due for completion in autumn 2008, said Simon Fairman, Grain LNG Importation Terminal manager. A Phase III expansion, which is planned to come on stream 2010/11, is currently in the final stages of negotiation with a decision expected this summer, he also pointed out.

For phase II, EPC contractor CB&I’s remit is to increase the gassification and sendout capacity and the boil-off gas handling capacity. The contract also includes the installation of a new control and administration facility and related systems.

The developments at Grain LNG reflect an increasing awareness by the gas supply industry of its reliance on imports as the North Sea gas diminishes. UK gas production is forecast to go into steep decline over the next few years and the country is already a net importer of gas. But incremental changes in the quantity to be imported are predicted. Indeed, the UK will import 46% of gas demand by 2010 and 67% by 2014, industry figures indicate.

Grain LNG’s first contract is held by a joint venture between BP and Algerian gas producer Sonatrach, and enables them to import 3.3 mtpa through the terminal over the next 20 years. This is equivalent to 4.4 billion cubic metres per annum or 12 million cubic metres a day of gas entering the National Transmission System (NTS).

“BP/Sonatrach decides when to put gas into the tanks. The contract specifies 140gwh of capacity but can go up to 186GWh if required. We are tied into open market as we only offer the regassification, therefore allowing the customer much more flexibility. We never own the LNG or the gas,” explained Fairman.

LNG is shipped in to the terminal from Trinidad, Algeria, Egypt and Qatar. Almost all of the approximately 60 shipments to the Isle of Grain to date have been via Membrane tankers — which feature giant double-wall metal containers and typically transport about 125,000m3 of LNG. The carriers dock at the jetty unloading station, which has three 16-inch loading arms and a 16-inch vapour return arm. These feed the gas into a pipeline system comprising a single 36-inch line with a 14-inch LNG recirculation line.

These 4.5km-long pipelines — including expansion loops that allow movement as the pipe cools down — sit above ground on concrete sleepers. As well as transferring the LNG, the cryogenic pipelines are designed to manage flash gas surge and heat ingress issues during the initial stages of the offloading procedure, said Culkin.

The main line consists of 400 welded pipe sections with only two bolted flanges — at the jetty and the base of the storage tanks — to optimise its integrity.

The pre-insulated pipes — a nickel-steel construction insulated with flexible PUR foam insulation — is designed to transmit the forces induced by the thermal contraction of the steel pipe to the HDPE casing, Culkin continued. The pipelines are also run full and cold to prevent thermal cycling of the pipeline, he added.

Grain LNG employs four 38-bar compressors for unloading the ship and two 2-bar units for day-to-day operations when not unloading. The compressors operate at suction temperatures down to -160°C — the gas exiting at 135°C and then passed through a superheater to reduce its temperature to around 5°C.

The submerged combustion vaporisers feature a combustion burner in a water bath to vaporise LNG as it passes through a stainless steel ladder, tubular heat exchanger. Gas outlet temperature is around 5°C and achieves outputs of 17-170 tonnes/hr.

According to Culkin, the composition of some of the LNG imports does not exactly meet UK natural gas specifications and so requires nitrogen ballasting — the injection of nitrogen into the gas.

An Air Products plant at the site supplies nitrogen to help adjust the gas to specification. The plant generates around 300 tonnes of gaseous nitrogen per day and is backed up with a 1000-tonne liquid nitrogen storage facility.

The phase I expansion involved a major upgrade of the four existing 200,000m3 LNG storage tanks. These 9% nickel-steel, double-containment tanks are heavily insulated with Purlite to store LNG at -162°C at 100mbarg.

During the phase I modification, the tanks — around 54 metre high and 50 metre in diameter — were fitted with new pressure relief systems and new level, temperature and pressure instrumentation for importation duty. While out of service, the tanks were also inspected and revalidated for 20 years.

With regard to safety, Fairman said the company had been running for over 27 years without any major accident or loss of containment. He also noted, there have been over 72,000 sea voyages delivering LNG to sites worldwide.

LNG is an asset intensive business with a lot of continuous effort to drive change and improvements, not least in safety, said Fairman. “We live and breathe safety. We are very closely regulated and very serious about the safety of the terminal, of everyone working here and of the community around us.”

People working here know that they are responsible for their own safety and the safety of those around them. New recruits undergo a 26-week training before they are allowed to work unsupervised at the site, Fairman commenting: “It isn’t acceptable to put people out there without everyone being fully aware of what is going on.”

Grain LNG’s workforce will double to 100 when phase II comes on stream, said Fairman, who noted that “LNG skills have become very tight with a lot of major projects coming on worldwide.” New recruits, he said, will include graduates and specialised engineers, as well as trainees sourced from the company’s work with local schools, according to the terminal manager.

Reviewing control and automation systems, Culkin said: “We inherited a range of control systems for different functions. We have now moved everything over to Honeywell’s Experion system.” The system enables operators to view plant-wide operations from a single control room and automatically generate critical information such as daily gas send-out, and gas reconciliation data. The next target, said Culkin, is to link the DCS data closer to the business information systems to support the site’s responsiveness to the daily peaks and troughs the UK gas demand.

Grain LNG’s priority is the safe delivery of energy on behalf of its customers, concluded Fairman. The vision, he said, “is to be the world’s leading LNG importation business. Its role in delivering gas export flexibly to its customers and meeting rigid gas quality specification