[Oil&Gas] (LNG) Paper" Energy Efficient LNG Production @ Tangguh LNG Plant" by Abang Daya Wigunan BP Ind (bagian 1) akan di presentasikan dalam Expert Sharing tanggal 31 Januari 2015 @ KMI Training Centre BSD City

[migas_indonesia@yahoo.com [Migas_Indonesia]]

 

Migas Indoonesia

Saya posting tulisan Pak Abang Daya Wiguna dari BP Indonesia sebagai bahasan untuk diskusi dalam Expert Sharing Tanggal 31 Januari 2015.

Salam Migas

S Herry Putranto

Administrator

First Presented in Gastech - London, 2012

Energy Efficient LNG Production

Abang Daya Wiguna, Boris Ertl, Dugald Wright

BP Indonesia

Keyword: LNG Plant, open-cycle system, liquefaction, energy efficiency, steam gas turbine

Abstract

The Tangguh LNG plant in Papua Barat, Indonesia employs innovative heat and power integration, delivering a step change in energy efficiency compared to conventional open cycle liquefaction.

Now that the plant is operational, the actual energy efficiency has been studied to gather the data needed to optimise lifecycle energy performance.

The liquefaction facilities at Tangguh produce 7.6 MTPA of LNG from a lean gas feed, with four

Frame 7 gas turbine drivers powering two C3MR technology liquefaction trains, in a split-MR configuration (APCI license). Waste heat from the gas turbine drivers produces high pressure steam which provides energy to steam turbine starter / helper drivers on the refrigeration compression strings, and electrical power generation at the site. Low pressure steam, predominantly extracted from the steam turbine drivers, provides the process heating requirement - notably for the acid gas removal unit. Utility boilers are installed for start-up loads, and to make-up steam in operation; maintaining the heat and power balance of the complex. This configuration has a number of environmental and operating advantages over conventional open cycle systems, including:

• lower fuel use and CO2 emissions
• turbines with steady high loads - maximising efficiency and minimising emissions (including NOx)
• reduced electrical power infrastructure, due to some key drivers provided by steam turbines
• high stored energy in steam drums & headers result in good system stability and robust transient response behaviour

Measured fuel use during the performance test of the Tangguh LNG plant was equivalent to approximately 0.23 tonnes CO2 from combustion gas per tonne of LNG exported. A recent energy review has trended actual energy consumption over a longer period, and confirmed that despite the hot location and very lean feed gas, energy consumption has averaged below 4.5 MMBtu per tonne of LNG exported (below 0.24 tonnes combustion gas CO2 per tonne of LNG exported.)

Heat and power integration brings tangible benefits to liquefaction plant design and operation.

These benefits come at the price of increased complexity though, due to integration between process and utilities systems, and a potential increased impact of "common mode failure", in which a steam system failure has a significant impact on the overall plant operation. However, on balance the benefits dominate, and a similar integrated heat and power concept is planned to be deployed to the Tangguh expansion project and other future LNG developments.

Introduction to Tangguh

Overview

Tangguh LNG is the third LNG export hub in Indonesia. In March 2005, Government of Indonesia gave the go ahead for the Tangguh LNG project in the Bintuni area of West Papua. The project is now in operation, with first LNG cargo exported on the 6th July 2009.

Tangguh plant is located 3,200km from Jakarta, in the Bintuni Bay area of Papua, Indonesia. Facilities include the LNG liquefaction plant in Bintuni Bay, a field office in Babo, and liaison offices in Sorong, Manokwari, Bintuni and Fak Fak. With 37.16% interest in the project, BP Indonesia is the operator of Tangguh under a production sharing contract with SKKMIGAS.

This project has combined sensitivity to the unique local environment and cultures, attention to process safety and sensitivity to the global environment through an innovative, energy-efficient design.

Tangguh’s innovative heat and power integration has delivered energy efficient LNG production by reducing the consumption of fuel. Energy recovery through the implementation of a combined cycle system, typical in power generation applications, has been successful in enhancing LNG plant efficiency.

Figure 1: Tangguh LNG Plant Location

Facilities description

Tangguh facilities on Vorwata field comprise:

• 15 offshore wells in the Vorwata gas field
• 2 offshore NUI (normally unmanned installation) platforms and 2 sub-sea 24” pipelines
• Onshore receiving and gas conditioning facilities
• 2 x 3.8 Mt/y LNG liquefaction trains driven by 2 (two) Frame 7GE gas turbine
• LNG and condensate storage and marine export facilities
• Integrated utility systems and Infrastructure

LNG process design features

The trains are designed based on technology licenses from BASF (acid gas removal) and APCI (LNG liquefaction). The liquefaction technology used is propane pre-cooled mixed refrigerant, driven by two Frame 7GE gas turbines with steam turbine starter. Shaft power is roughly balanced in two refrigerant compression strings by splitting the mixed refrigerant (MR) compression: one string has the propane compressor and the high pressure MR compressor; the other has the low pressure and medium pressure MR compressor. Few design features are incorporated to deliver less equipment, including:

• No end flash compression system. LNG flashes in the tanks, generating sufficient flash gas and boil-off gas to supply the fuel gas demand.

• No dehydration regeneration gas recompression. Tangguh uses boil-off gas for molecular sieve bed regeneration. Spent regeneration gas is then used as fuel.

Heat and power integration

Recent LNG plants utilising large industrial gas turbine drives, typically GE Frame 7 machines, have used large electrical helper / starter motors requiring a large power plant to provide the electricity. At Tangguh there is no separate power plant. Instead, heat is recovered from the gas turbine exhausts to generate steam which then in turn provides the motive force for steam turbine compressor starter / helpers and steam turbine generators for electricity production. Low grade steam exiting the starter / helper steam turbines is used to provide process heat, primarily in the acid gas removal unit.

The feed gas to the plant has a relatively high acid gas content (typically 12% CO2) which results in a high heat requirement in the acid gas removal unit. This high process heat duty provides a sink for low grade heat which has enabled an overall high cycle efficiency of the plant, of approximately 55%.

The efficient utilisation of waste heat from the Frame 7 EA gas turbines by raising high pressure steam allows the Tangguh LNG plant to deliver higher plant efficiency through combined cycle operation. High pressure steam is used to provide motive power to the refrigeration compressors and generators; low pressure steam provides process heat to AGRU re boilers and other process heaters.

Figure 2: Overview of onshore process facilities

As with all LNG liquefaction plants the power demand at the site is variable, depending on transient demands such as ship loading. The steam balance is designed such that all steam generated by the heat recovery steam generators (HRSGs) is consumed by the process, with variable make-up of steam to maintain the heat balance from 3 package boilers [150 t/h each]. The boilers are also required for start-up, providing steam in advance of waste heat being available from the HRSGs.

A typical Tangguh LNG plant energy balance during is shown in Table 1 below, based on operating data at a time when total heat and motive power demand was 664 MW, with approximately 50% of the energy demand supplied through waste heat recovery.

Figure 3: Block flow diagram of Tangguh onshore process facilities

Figure 4: Tangguh LNG integrated heat and power concept

Note that the AGRU heat duty makes up approximately 80% of the total process heat duty. The integration of HP steam producers through waste heat utilization and LP steam consumers in AGRU and other process unit allows Tangguh LNG plant to significantly reduce the fuel consumption for fired equipment to supply this heat duty.

The Tangguh LNG plant uses steam as a heating medium, primarily comprising:

• HP steam at 40 kg/cm²g and 400°C used for motive power and electricity generation via steam turbine drivers & generators
• LP steam at 3.5 kg/cm²g and 148°C used for process heat

Almost 730 t/h of HP steam is generated to provide plant heat energy demand in 2 train operation. The majority of the HP steam demand is supplied by the heat recovery steam generators (HRSGs), with the balance being supplied by package boilers. As the total site power demand is cyclic, depending for example on ship loading vs. holding mode, the package boilers maintain operational flexibility.

Table 1: Tangguh LNG energy balance - typical operating data

(bersambung)

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