Optimising Liquefied Natural Gas Production with an Intelligent Valve Strategy
a report by Ron Baker1 and Tim Webb2 1. Sales Director, Severn Glocon; 2. Industrial Gas Products Sales Manager, Severn Glocon
Annual global production of liquefied natural gas (LNG) continues to expand at a phenomenal rate. Figures released by the consultancy Evaluate Energy in 2011 show that global capacity has risen 60 % to 260 m tonnes/year and this is projected to increase by a further 50 % over the next five years.
Safety and Productivity
This exponential increase in production comes with a host of associated issues, not least safety. If you talk to anybody who works with LNG – regardless of whether they are based at one of the new mega plants in South East Asia or at an older facility – they will tell you that safety is their paramount concern. Natural gas is a hugely volatile medium, particularly during and prior to the ‘sweetening’ phase of liquefaction when exceptionally unstable or corrosive elements can be present.
Safety is inextricably linked with other important factors such as productivity and supply chain management. Indeed, safety and productivity have an almost symbiotic relationship. Each of these elements depends on the performance of key assets involved in the liquefaction and regasification processes. Furthermore, valves, although a relatively small component in themselves, touch on all major assets within a plant, playing a vital role (see Figure 1).
The number of globe and angle-style control valves on a liquefaction plant is relatively small, compared with, for example, a refinery of similar dollar value. However, the proportion of engineered severe service valves is high. Furthermore, it is widely accepted that severe service valves can be a major culprit when it comes to the number one threat to LNG plant safety and performance: fugitive emissions. Once leakage begins the problem can escalate quickly. It is not unheard of for a valve- related emissions incident to lead to 48 hours of plant downtime,
Ron Baker is Sales Director at Severn Glocon. He has 35 years experience in the oil and gas industry and is an industry graduate in Industrial Measurement and Control. He has been involved in 13 LNG projects.
E:
ron.baker@
severnglocon.co.uk
leading to serious consequences for production and supply-chain management. Emissions pose a risk to the safety of people working at the plant or terminal, as well to the surrounding environment and are a surefire way to lead to plant shutdown, sending shock-waves up and down the supply chain and bringing huge financial implications.
For LNG plant managers, valves are more than just a commodity. They are highly engineered precision tools that are mission-critical to LNG plant performance and safety.
A Spotlight on Valve Performance
Traditionally, much activity to enhance valve performance and minimise the risk of emissions begins and ends with the stem. Given that this area of a valve can sometimes be vulnerable to leakage, a small but significant tactic is to improve stem finish and packing designs. However, to truly reduce the potential problems, the entire valve needs to be highly engineered, not just the stem (see Figure 2). Furthermore, the valve needs to be considered in the context of the plant as a whole.
Minimising the risk of valve-related fugitive emissions in the long-term requires a holistic and intelligent strategy. This begins with the specification of valves and incorporates their design, manufacture and installation. It also needs to move beyond this to consider ongoing management and maintenance routines across the entire valve population throughout its lifetime.
Specification to Installation
LNG processing requires design temperatures of -175 °C and involves operating temperatures as low as -158 °C. The challenges of this sector have led to the development of industry standards dictating that cryogenic testing (see Figure 3) must be performed on ‘one valve per size per type’ before delivery to site. When such rigorous methods are also employed through the wider valve commissioning and installation process, it goes a long way towards cutting the risk of emissions, while enhancing overall safety and performance.
Tim Webb is Global Sales Manager for LNG and industrial gas applications and has been with Severn Glocon for over 26 years. Having originally worked in Severn’s Engineering Design Department for eight years, he joined the sales force in 1993 and headed up the LNG/industrial gas business in the year 2000. Prior to joining Severn, Tim completed a five-year Technical apprenticeship with the valve group Hattersley Newman Hender in Woodchester, Stroud.
E:
tim.webb@severnglocon.co.uk
The harsh demands of LNG applications mean that every valve needs to receive a robust, bespoke specification. For instance, thermal dynamics must be taken into consideration to ensure that valves are suitable for cryogenic conditions. The materials used are determined by the low operating temperatures – carbon steel is inappropriate, but stainless steels are commonly used for most parts. Specification should also pay attention to the various operating conditions across the plant: the working pressures at different points in the process, the sizes of valves required and the best methods of actuation.
It is also important that the application challenges facing each valve are thoroughly understood. This is particularly true of valves involved in the sweetening activity prior to liquefaction (when operators are
62 © TOUCH BRIEFINGS 2011
LNG
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