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Gastech 2005

Gastech 2005

Bilbao, Spain

Paper

Design and Safety Considerations for existing LNG Peak Shaving Plants

Presented by

Hans Joachim Grossmann

Director

GOC Engineering GmbHBachovenstr. 8

53489 Sinzig, [email protected]

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Gastech 2005 Grossman 2

1. Abstract

Starting from the mid 70`s many LNG Peak Shaving Plants and Terminals has been constructed and commissioned invarious locations worldwide. During these 30 years many regulations were changed considerably in respect of morestringent safety and environmental requirements. Furthermore technical standards have been further developed withprocedures of identifying and assessing process hazards. Owner and Operators of old LNG plants and terminals are nowfacing several questions in regard of their own plants to introduce revamping and life extension programs. To complywith state of the art of safety and operational standards within the LNG plant is already the ignition of detailed technicaland economical discussions and evaluations.

This paper focuses on a properly analysed situation for an existing LNG peak shaving plant in Germany and thecooperation of Owner and Engineer to increase safety and plant operations. The complete project phases from the initialsafety study to the decommissioning of the systems will be presented. Up dated information of the status of execution ofworks is given.

The contents of the paper can be a helpful and useful tool for owners, operators and engineers of similar plants ormarine terminals for loading, storage & handling facilities of liquefied hydrocarbons.

2. The PlantThe LNG Peak Shaving Plant, located at Dormagen-Nievenheim, Germany is part of the natural gas transmission andstorage network owned by RWE- Energy. The company serves imports natural gas for more than 30 years to their

customers. Imports include gas supplies from The Netherlands, Norway, Russia and the UK. The pipeline grid includesmore than 4,000 km of underground high pressure pipelines.Compressors booster stations keep the gas moving, blending stations are provided for mixing gas of varying grades (higho low caloric grades). For reserve stocks of gas mainly cavern storages are used.

Aboveground storage facility is provided at the peak shaving plant in Dormagen-Nievenheim. The plant is beside of anLNG peak shaving plant in the south of Germany the only cryogenic LNG storage facility in Germany.

a. Brief Plant Descript ionThe main plant operations are described as follows:

Gas Treatment and LiquefactionGas to be liquefied for storage is taken from the transmission mains and reduced to 40 bar. It is passed through twoabsorber systems to remove moisture, aromatics and carbon dioxide. A further separator cleaned the gas from heavyhydrocarbons (HHCs)For the liquefaction process a Mixed Refrigerant Liquid (MRL) cycles is used as coolant. Flash gas is utilized together withthe separated heavy hydrocarbons to clean the adsorber bed before being returned to the pipeline.

MRL is a Methane/Propane mixture

Liquefection capacity 2,400 Nm/h

Plate type heat exchanger is used as main process heat exchanger and a reciprocating compressor is used to compress

flash gas and MRL. Previously the compressor was used to condition the send out gas back to pipeline gas quality.

Stages: 8Power: 1, 9 MWPsuc: -0,1 / +0,2 barPdisch NG (4. stage): 67,5 bar

MRL (3. stage): 54 barCapacity NG: max. 6.145 Nm/hCapacity MRL: max. 6.820 Nm/hMaker Ingersoll Rand

Storage of LNGThe LNG is stored in a double wall steel tank made out of 9% nickel steel for the inner tank and carbon steel for theouter tank known as single containment storage system.The discharge pipeline is designed as bottom outlet from the tanks. Filling line is connected to the liquid phase too.The tank is enclosed by an earth embankment capable of containing the entire liquid contents of the reservoir.

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Geometrical capacity of the tank: 22,700 m (say 14 million Nm gas storage capacity)Design pressure: 68 mbarDesign code: API 620 Q in combination with DIN 4119 and German pressure vessel rules (AD).

BOG handling systemThe boil off gases are reliquefied by compression, refrigeration and expansion and routed back to the tank. Therepeated circulation is used for homogenization of the tank contents.

Natural gas send out system

When the reserve of liquefied gas is required for distribution at time of peak demand, it is first pressurized by two highpressure pumps to equal the pipeline pressure, which may be as high as 70 bars.To bring the calorific value of the send out gas in line with the pipeline gas liquid nitrogen is added before the LNG isvaporized in two submerged combustion vaporizer.

Send- out rate 2 x 50,000 Nm3 /h

Truck loading systemTo serve various costumers with LNG a single truck loading bay is installed

Send out rate 35 Nm/h

History

The plant was built by CBI Germany in 1974/75 and commissioned in 1976.It was continuously in operation since nearly 30 years.

The plant is subject to regulations covering hazardous industrial sites and must be conform to the highest level of rules &regulations as laid down in the provisions of national emission control laws.

3. Project PhasesMain driver of the project was that the client wants to operate the plant for the next 20 years considering that the plantshall in line with the relevant rules & regulations.Furthermore the German laws handover the responsibility for state-of-the-art in safety to the plant operator.

a. Conform it y Study Rules & RegulationsThe aim of this initial study, carried out in 2002 was to clarify the actual status of the plant with respect to

Status of installed active and passive safety equipment including review of existing documentation To check the compliance of the plant with the actual rules & regulations, especially for the LNG Tank

For LNG Installations two main codes & standards are followed for new LNG storage plants

NFPA 59A - Standard for the production, storage and handling of liquefied natural gas EN 1473 Installation and equipment for liquefied natural gas

Tank penetrations

EN 1473 allows no penetrations of the primary and secondary container walls, means the requirement of the use ofsubmerged pumps.NFPA 59A allows penetrations, however the design spill shall be calculated as the full liquid content of the tank.The design spill in case of the use of submerged pumps (over the top fill and emptying) results in 10 min operation of theinstalled pumps capacity.

ResultThe main topics which arises out the study was

Renew the field instrumentation and the control system ( fail safe instrumentation) due to the age of theequipment

Review the LNG tank design with respect to tank nozzles at bottom at shell below the liquid level. Review the consequences of the installation of submerged pumps( reduces hazard arising from LNG) Review the consequences of the installation of additional safety features (e.g. water curtains, foam system,

thermal insulation of impoundment area) to reduce the evaporation and dispersion of spilled LNG.

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b. Costing StudyBased on the results of the above mentioned study a detailed costing study was carried out with the main alternatives

Installation of submerged pumps Installation of additional safety features without submerged pumps Revamping of the entire plant (Instrumentation, Control system, mechanical equipment etc.)

ResultBeside the costs for revamping of the entire plant the estimated costs for installation of submerged pumps are just 10 %

higher than for the installation of additional safety feature

With consideration of all aspects of the alternatives and having in mind that with the installation of submerged pumps theLNG peak shaving plant shall comply with the latest codes & standards also in future it was decided to install submergedpumps.

4. The ProjectEnd of 2003 the engineering work starts for the entire project including the following main area

Decommissioning of the LNG tank/plant Modification of the LNG tank to install submerged pumps Renewing of instrument & control system including increased Level of Automation New BOG Handling System ( was added to the project 1Q/ 2004) General Revamping of the plant including the supply of new apparatuses, valves piping

system, Extension of the existing control building)

Project scheduleThe overall project schedule is based on the fact that the peak shaving plant must be back in operation for the winterseason 2005/2006.

5. Design Aspectsa. Static Calculation of existing Tank

A new static calculation was required to confirm that he tank structure can handle the added loads due to

the installation of a new pump platform on the tank roof the installation of new pump columns inside the tank

Secondly the existing tank was recalculated due to the actual codes and requirements for this type of tank structure inGermany. The calculation results in a recommendation to install a additional stiffener ring at the outer tank shell.

All calculations were made with FE methods using the latest version of ANSYS software package.

b. Submerged pumpsThe tank shall be equipped with two submersible, retractable pumps. The existing pumps will be further utilized so thatthe submerged pumps acting as low pressure feed pumps.Of major importance during design stage was to have a low energy input into the tank to avoid an increased boil off.By selection the pumps low weight, small diameter was considered to avoid too much modification work for the tank

structure itself.

c. HAZOP Study/Safety ReportA coarse HAZOP study was prepared already in 2003 to combine the operation experiences of the plant operators withsafety requirements due to the installation of new field instrumentation and new control system.To serve the requirements of the local authorities the safety report of the plant including risk assessment need to becompletely revised.

d. Process optimizationThe revamping of the plant is use also to optimise the process of the systems. Process simulations support thisoptimization in close contact with operators and makers of equipment.

e. Increased level of automationA complete revamping of the field instrumentation is underway including an increased level of automation for variousoperations e.g. gas treatment and liquefaction, BOG handling, send out system. This includes modern DP/PA Busstructures, remote control and operation of the processes by using field workstations. A number of hand valves arereplaced by remote operating valves.

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f. BOG HandlingThe existing BOG handling system which included partially reliquefaction of BOG back to the tank shall be replaced by adirect BOG handling system just to suck the BOG from the tank and send it via a three stage piston compressor to thegas pipeline grid.

6. Project Executiona. Decommissioning of LNG tankThe plant was taken out of operation in March 2004 with a liquid level of approx. 2, 5 m of LNG in the tank. This was dueto the fact that no proven information was available for the NSPH performance of the existing high pressure pumps.

Therefore it was decided to stop at this point and to install a temporary connection to the LNG pump which was installedto load road tanker. The normal capacity of this pump was similar to the estimated minimum flow of one high pressurepump.With this temporary feed pump the tank was more or less 100% liquid emptied in a very smooth and safe operation.The LNG was pumped out using the normal send out way via the vaporizers.

b. Warming up/Purging of TankAfter natural warming up of the tank, it was purged with nitrogen at a rate of 300 350 m/h using nitrogen road tankerfacility. Total nitrogen consumptions were approx 6 times of the tank volume. Purging with air follows to allowinspection of the tank.c. First Tank Opening after 30 YearsThe first opening of the inner tank after 30 years of continuously operation of the tank was on September 07, 2004.

d. Tank InspectionIn accordance to German Law the tank was inspected by a Third Party (TUEV). The inner tank was visual inspected; thebottom was tested with a vacuum box. Plate thicknesses of inner and outer tank /shell roof were tested.

A piece of the bottom outlet structure was tested in a laboratory to check the chemical analysis and the mechanical,technological data.The results of all tests and inspections were satisfied and no unexpected findings were detected.e. Safety Aspects

All project phases to date are carried out under a high safety standard monitored and controlled by an independentsafety inspector.

7. Proj ect Statu sThe actual project status per February 2005 is as follows (picture will be show during paper presentation:

a. LNG Tank Installation of additional shell stiffener are completed Preparation for the Installation of the new pump platform Pump/Level/Temperature columns prefabricated Submerged pumps ready for performance test

b. BOG System BOG Compressor ordered

c. Instrumentation & Control Field construction work ongoing Fabrication of PLC/Control System

d. Mechanical Work/Civil work starts8.

Proj ect Organisat ion

The project organisation follows the following framework

One engineering contractor for the entire project Direct purchasing of equipment and /or construction services

The overall project costs are in the range of 13 Million.

9. Summary/ Conclusion/ OutlookWe are aware that the statements in this paper are only touching a part of the very complex execution of revamping anLNG facility. However the project phases as described above can be adapted for similar projects too.The project of revamping the LNG peak shaving plant at Nievenheim stand as an example of trustful and closerelationship between the Clients, Engineer and Maker. Mainly the decision of the client to develop the project stepwise incooperation with an experienced process orientated Engineer results in a smooth and safe project execution. Asengineers and consultants of process plants we see our responsibility in providing this type of expertise.

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We hope that we can have the opportunity during the next GASTECH event to report to the audience the nextimportance project phase, the Re-start of the the LNG peak shaving plant back into operation.

10 . Pictur es/ Diagrams

Picture 1 - Overall View - LNG Peak Shaving Plant Nievenheim

Picture 2 - HP LNG Send out pumps

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Picture 3 - LNG Vaporizer

Pictur e 4 Temporary Feed connection bet w een HP pump and Road tanker pump

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Pictur e 5- Pict ure made by Thermo gr aphic camera to detect defect s in insulation ( made during empt yingof tank)

Pictur e 6 Nit rogen vaporizer

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Pictur e 7 Bott om out let LNG Tank

Picture 8 LNG Tank above suspended deck

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