SPE 83977 Twister Supersonic Gas Conditioning for Unmanned Platforms and Subsea Gas Processing J.M. Brouwer, H.D. Epsom / Twister BV (www.TwisterBV.com) (www.TwisterBV.com)
Copyright 2003, Society of Petroleum Engineers Engineers Inc. This paper was prepared for presentation at Offshore Europe 2003 held in Aberdeen, UK, 2-5 September 2003. This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435. 01-972-952-9435.
Abstract Twister is a revolutionary gas conditioning technology which has been under development for natural gas applications since 1997. Condensation and separation at supersonic velocity is the key to some unique benefits. An extremely short residence time prevents hydrate problems, eliminating chemicals and associated regeneration systems. The simplicity and reliability of a static device, with no rotating parts and operating without chemicals, ensures a simple facility with a high availability, suitable for unmanned operation. Full scale test units have been operational since 1998 at five gas plants in the Netherlands, Nigeria and Norway, with varying gas compositions and operating conditions. Test results have been used to improve and validate sophisticated Computational Fluid Dynamic (CFD) models of the complex combination of aerodynamics, thermodynamics and fluiddynamics. These CFD models have been paramount in improving Twister performance. Although Twister is a mature technology, Twister BV are developing a second generation Twister design promising a step change performance improvement and reduced pressure drop. Field testing is scheduled for early 2004 with market launch later that year. The first commercial Twister application will start-up in the 4th Quarter of 2003. Twister has been selected for the dehydration process of a large, offshore gas development in Malaysia. The Twister system design will be described. Its simplicity makes Twister a key enabling technology for subsea gas processing. The results of a joint industry feasibility study will be reported.
Introduction Twister is a revolutionary gas conditioning technology which can be used to condense and separate water and heavy
hydrocarbons from natural gas [1]. Current applications include: 1. Dehydration 2. Hydrocarbon dewpointing 3. Natural Gas Liquids extraction 4. Heating value reduction New applications under study include offshore fuel gas treatment for large aero-derivative gas turbines, pre-treatment upstream CO2 membranes and bulk H2S removal upstream sweetening plants. The Twister Supersonic Separator has thermodynamics similar to a turbo-expander, combining expansion, cyclone gas/liquid separation and re-compression in a compact, tubular device. Whereas a turbo-expander transforms pressure to shaft power, Twister achieves a similar temperature drop by transforming pressure to kinetic energy (i.e. supersonic velocity). Expander
Cyclone Separator
Compressor
Saturated Feed Gas
Dry Gas
100 bar, 20C (1450psi, 68F)
30 bar, -40C (435psi, -40F)
Laval Nozzle
Supersonic Wing Mach 1.3 (500 m/s)
70 bar, 10C (1015psi, 50F)
Cyclone Separator (300,000g) Diffuser Liquids + Slip-Gas
70 bar, 0C (1015psi, 32F)
Figure 1 - Cross-section of the Tw ister tube
Error! Reference source not found. shows the basic design concept: 1. A Laval nozzle is used to expand the saturated feed gas to supersonic velocity, which results in a low temperature and pressure. A mist of water and hydrocarbon condensation droplets will form. 2. A wing placed in the supersonic supersonic flow regime will generate a high vorticity swirl (up to 300,000g), centrifuging the droplets to the wall. 3. The liquids are split from the gas using a cyclone separator. 4. The separated streams streams are slowed down in separate diffusers, recovering some 65-80% of the initial pressure. 5. The liquid stream still contains slip-gas, which will be removed in a compact liquid de-gassing vessel and recombined with the dry gas stream.
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Benefits Condensation and separation at supersonic velocity is the key to some unique benefits. A Twister tube designed for 35 MMscfd at 100 bar is only 2 meters long inside a 150 mm casing. The residence time inside the cold Twister Supersonic Separator is only milliseconds, allowing hydrates no time to form and avoiding the requirement for hydrate inhibition chemicals. The elimination of the associated chemical regeneration systems avoids harmful BTX emissions to the environment. The simplicity and reliability of a static device, with no rotating parts and operating without chemicals, ensures a simple facility with a high availability, suitable for unmanned operation in harsh and/or offshore environments. The compact and low weight facilities can be installed on an unmanned, minimum facilities platform, not much larger than a simple wellhead platform.
System design Figure 2 shows a process flow diagram of a typical Twister system. Twister is a Low Temperature Separation (LTS) process, which performance can be optimised by inlet cooling. This can be achieved by heat integration using the cold gas exiting Twister, supplemented with air or seawater cooling if required. The inlet separator upstream of the Twister tubes is designed to remove produced liquids and prevent carry-over of slugs and solids. The gas from the inlet separator is then directed through the Twister tubes. The liquids separated by Twister will still contain slip-gas, some 20-30% of the total gas stream, which will be removed in a liquid de-gassing vessel and recombined with the dry gas stream.
•
•
will include multiple Twister tubes to provide the required turndown flexibility. Twister is a pressure ratio device. For any design pressure, the gas will expand to typically 30% of feed pressure mid Twister and recompress to 65 to 80% of feed pressure at the exit of Twister. The supersonic conditions inside the Twister tubes are intolerant to solids. Careful design of the inlet separation system will be required to capture solids larger than 15 microns.
LTX liquid de-gassing vessel Typically, the operating conditions of the liquid de-gassing vessel are well within the hydrate formation regime. Twister BV has developed a compact and highly efficient vessel design based on conventional LTX technology, using heating coils to melt the hydrates. A prototype of the improved and proprietary LTX design has been commissioned at the NAM operated Leermens plant in the Netherlands early 2002 and performance testing has been successfully completed early 2003.
Twister Tube(s)
Gas/Gas HEX Inlet Separator Air/Sea water Cooler Liquid De-Gassing Vessel Water & Condensate
Figure 3 - Vertical Twister-LTX pilot plant in the Netherlands
Field test results Figure 2 - Process flow diagram of a Twister system
The dry gas from the Twister tubes is mixed with the gas from the liquid de-gassing vessel and directed through the gas/gas heat exchanger to cool the feed gas. The water and hydrocarbon condensate from the inlet separator and liquid degassing vessel will typically be routed to a coalescer to remove free water from the condensate. In designing a gas conditioning system based on Twister technology, the following issues need to be considered: Twister is a fixed actual volumetric flow device. The gas • velocity at the throat of the Laval nozzle will always be exactly Mach 1, fixing the flow through the tube. Some turndown flexibility can be achieved by adjusting the operating pressure. However, a typical Twister system
Although Twister is a relatively new technology, extensive operating experience has been obtained with commercial scale test units in five different gas plants in the Netherlands since 1998, in Nigeria since 2000 and in Norway since 2002. These test units have proved the viability of gas conditioning to typical pipeline specifications as well as suitability for unmanned operation. The Twister plant in Nigeria has been in operation since November 2000, successfully dehydrating 30 MMscfd to pipeline specification (5°C water dewpoint at 70 bar export pressure). In total six different Twister tubes were tested in Nigeria. These design iterations were required to expand the operating envelope of Twister and the validity envelope of the Twister design models from lean to rich gas compositions, since the Utorogu gas composition is significantly richer than any gas
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tested before. In addition, problems were initially encountered with the accuracy of test measurements, necessitating the development and installation of sophisticated measurement systems including on-line water and hydrocarbon (HC) dew point metering. The latest test results in Nigeria showed a particularly good water dew pointing performance, with an effective water dew point suppression of approximately 22-28°C (40-50ºF). Based on a typical feed temperature of 20°C (68ºF), operating just outside the hydrate regime, the effective water dewpoint of the gas exiting Twister is -2 to -9°C (18 to 28ºF), confidently meeting the water dewpoint specifications of both the onshore and offshore Gas Gathering Systems in Nigeria. HC dewpointing performance has proved more difficult to validate since 2-phase flow occurred at the point of measurement which could only be operated at 10 bar (145 psi). However, the addition of a simple separator ensures the HC dewpoint specification of 15ºC at 80 bar (59ºF at 1,160 psi) will be met. Note that the HC dewpointing performance of Twister strongly depends upon the gas composition and process conditions. Over the complete testing period Twister has been operated without glycol injection. The elimination of glycol and its associated regeneration systems, combined with the absence of rotating parts, has demonstrated a step change improvement in simplicity and reliability, critical factors enabling normally unmanned operation. Studies indicate that Twister can typically reduce life cycle cost by 10-25% compared to conventional technologies such as Joule Thompson expansion and mechanical refrigeration. The Shell operating unit in Nigeria (SPDC) now plans to relocate the Twister plant for a commercial fuel gas conditioning application. Further commercial applications in Nigeria are under study, including an expansion of the Utorogu plant. Inlet temperature [F] 50
60
70
80
90
100
110
30
Figure 5 – CFD plot of the supersonic flow inside Twister. The colours represent pressure. The white triangle is the supersonic wing “twisting” the gas. The pipe-in-pipe separator is on the right.
Twister BV has now established in-house, world-class CFD modeling capabilities. CFD modelling has become an inherent part of the Twister design process. Testing at Utorogu has enabled Twister BV to expand the operating envelope of Twister, and the validity envelope of the Twister design models, from lean to rich gas compositions. Twister tube designs can now be confidently made for a wide range of gas compositions and process conditions without the design iterations experienced in Utorogu. Although Twister is a mature technology, Twister BV has an extensive research and development program in place to further improve the Twister performance envelope. An exciting development is the second generation Twister technology (patents pending). Principle improvements include enhanced separation efficiency due to higher vorticity and elimination of re-evaporation. Analysis with validated CFD models has been completed indicating a step change performance improvement allowing a significant reduction in pressure drop. Field testing is scheduled towards early 2004 with market launch later in the year.
85
HC dewpoint @ 10 bar (145 psi)
25
Offshore applications
75
H2O dewpoint @ 80 bar (1160 psi) 20 ] C [ t n i o p w e D
gas, resulting in a relatively high liquid loading inside the Twister tube. Computational Fluid Dynamics (CFD) models were used for the first time to design Twister tubes for Utorogu. Model calibration proved to be an iterative process, progressively improving the modeling accuracy and Twister performance. The CFD modelling of the liquid-rich multi-phase flow behavior inside Twister proved key to achieve further performance improvements.
65
15
]
55 F [ t n i
10
45 o
p w e
5
35 D
0 -5
25
-10
15
-15
5
10
15
20
25
30
35
40
45
Inlet temperature [C]
Figure 4 - Dewpointing performance of the Twister demonstration plant in Nigeria
CFD Modelling The continuing performance improvement achieved since testing the first Twister tube design mid November 2000 can be mainly contributed to advancing modelling accuracy of the supersonic, multi-phase flow behaviour inside the Twister tube. Twister operating experience before testing at Utorogu was limited to relatively lean gas. Utorogu produces a particular rich non-associated gas comparable to associated
The benefits of Twister are most apparent for larger offshore gas developments. Offshore gas developments have traditionally been developed using manned glycol (TEG) dehydration facilities. Ever increasing pressure on cost, personnel safety and environment is steadily pushing unmanned concepts such as wet gas evacuation for new gas developments. The simplicity of Twister Supersonic Gas Conditioning technology now enables unmanned operation of offshore dehydration and dewpointing facilities, ensuring single-phase export. Twister offers a cost effective, safe and environmentally friendly, development concept, eliminating many of the flow assurance risks and limitations involved with multi-phase wet gas evacuation. The term "flow assurance" covers a broad range of topics in multiphase hydrocarbon production systems, including flow behaviour, hydrates, wax, asphaltenes, emulsions, scaling, corrosion and erosion. Flow assurance is about ensuring a steady and predictable flow of product to meet business commitments. It includes some of the most important technical issues facing the oil and gas industry today such as:
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Multi-phase export limits both pipeline turndown flexibility and maximum pipeline size, sometimes necessitating multiple smaller diameter pipelines and often eliminating the flexibility to tie-in future developments. The pressure drop in a multi-phase pipeline can be • significantly higher compared to single-phase gas export and difficult to predict. The pressure drop across the Twister process (20-35%) may be more than compensated for by the reduced pressure drop in the export pipeline. Twister may also allow a lower pipeline design pressure. The corrosion and hydrate management system needs to • be extremely reliable since the consequence of pipeline failure will be severe. Combined with the complexity of multi-phase flow behaviour, generally a conservative approach needs to be adopted at an obvious additional expense. Expenses for conservatively designed (CRA) pipelines and costly slug catching facilities need to be balanced with operational constraints including pigging and ramp-up procedures. Routine pigging for liquid holdup and corrosion management is an inherently hazardous and cumbersome operation. The chemistry of the produced water, in combination with • the corrosion & hydrate inhibition chemicals, may result in operational problems such as chemical contamination & scale depositions. Costly vacuum desalination facilities may be required to manage glycol salt contamination and it’s associated operational and corrosion issues. Table 1 shows the capital expenditure for a large offshore Non-Associated Gas (NAG) development, comparing some typical gas developments options. Note that the incremental cost of the offshore Twister facilities is more than balanced by savings on the pipeline and onshore facilities, notably elimination of slug-catcher and chemical regeneration systems. Twister will be a particularly attractive option for corrosive service, i.e. for gas compositions with a high CO2 fraction, which may necessitate a Corrosion Resistant Alloy (CRA) export line. For non-corrosive service, Twister will generally start to become attractive for longer gas export lines. The principle limitation of the Twister process compared to chemical dehydration is the required pressure drop of 20-35% of the feed pressure. However, this may be more than compensated for by the reduced pressure drop in a single phase export pipeline. •
Capital Expenditure (Surface) 1,000MMSCFD 100m waterdepth
TEG
Platform
185
Wet Gas Wet Gas CRA CS 120
120
Scope
Twister
TEG
Wet Gas CRA
165
Manned
Pipelines (100km)
45
120
50
35
3x24" CS
Slugcatcher
35
35
35
-
Yes
Onshore treatment Total US$MM (%)
50
55
55
35
Gas/Liquid treatment
315
330
260
235
(121%)
Wet Gas CS
Twister
Unmanned
Unmanned
Unmanned
3x24" CRA 6" CS
3x24" CS 6" CS
48"CS 12" CS
Yes
Yes
No
Gas/Liquid Gas/Liquid treatment, treatment, MEG regen. MEG regen. (127%)
(100%)
Liquid treatment (90%)
Table 1 – Cost comparison for offshore gas development options
B11 Offshore Malaysia Petronas and Sarawak Shell Berhad (SSB) have signed a purchase order for two 300 MMscfd Twister dehydration trains to be installed on the B11 platform offshore Malaysia. Commissioning is currently well underway with start-up planned for October 20 The B11 gas is particularly corrosive with CO2 concentrations of up to 20 mol%, advocating a reliable dehydration process. The very high H2S concentration of 3,500 ppm is a hazard to personnel and another incentive for unmanned operation. The gas is feeding an LNG plant in Bintulu, making high platform availability a key requirement. For these reasons there was a strong drive to design the B11 platform as a normally unmanned facility. Feasibility studies comparing Twister with the original manned TEG dehydration concept concluded that Twister was a key enabler for unmanned operation. Potential capital and operating cost savings were quantified to be US$30-80 million, roughly split 50/50% capital/operating expenditure.
Figure 6 - B11 process flow diagram
Figure 6 shows a process flow diagram of the B11 gas dehydration system. Gas from the platform wells arrives at approximately 155 bar and is cooled from 125 to 40ºC using air-coolers. Further cooling to 25ºC is achieved by crossexchange using the cold gas exiting Twister. Note inlet cooling is limited by the hydrate formation temperature of 22ºC at 155 bar. An efficient inlet separator removes free liquids and solids down to 15 microns. The gas is then dewpointed using a total of 5x10% parallel Twister tubes in each of the two trains. The pressure drop across the Twister tubes is 30% or 47 bar. The condensate and water condensed and separated by the Twister process is de-gassed in a 3-phase LTX separator equipped with heating coils to melt hydrates. The free water in condensate from the inlet- and LTS separators is removed using a combination of tilted-plate and filter coalescers designed to meet 275 ppmV free water in condensate. The dry condensate will be re-combined with the export gas. Six compact Twister tubes (one spare), each with a capacity of 60 MMscfd, are mounted in a vertical position on an LTX type, vertical liquid de-gassing vessel (see Figure 7). The footprint of the Twister module is 3x3 meters.
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Figure 7 – Twister lay-out for B11
A prototype of the B11 Twister system design has been commissioned at the NAM operated Leermens plant in the Netherlands early 2002 and performance testing has been successfully completed early 2003 (see Figure 3).
Figure 8 – B11 Twister tubes and LTX assembly
Twister Subsea Gas Processing Simplicity and reliability are critical success factors in subsea applications. Twister scores high on both counts and is therefore widely recognised as the missing link for subsea gas processing and a key enabling technology for the development of currently uneconomical gas reserves. Twister BV, FMC Kongsberg Subsea and Shell Technology Norway have completed a joint study, sponsored by Demo2000 and Norske Shell, to investigate the feasibility of subsea gas conditioning based on Twister technology [2]. No show stoppers have been identified, even if the technology is still relatively immature for subsea application. Several components required for such a subsea processing plant need further development and qualification prior to installation and operation on the seabed.
Figure 9 – Subsea Gas Conditioning template including Twister module
The subsea gas conditioning template includes the following modules: Manifold structure including the manifold piping with tie• ins, the inlet cooler and the inlet separator. Twister unit with the Low Temperature Separator (LTX) • including electric heater, a maximum of 6 off Twister tubes and related piping and valves Seawater cooling pump unit with electric motor, installed • on top of a transformer unit. Control valve unit with control system and battery • back up Spare unit with space for future condensate • polishing equipment A water injection pump and a condensate polishing unit • are optional modules which are not included in the layout of the processing plant described. Three prospective gas field developments have been studied to quantify the potential CAPEX savings of Twister subsea gas processing compared to conventional development options. One development which will be discussed, is a large gas accumulation 150 km off the Norwegian coast which has a varying water depth of 700 to 1,100m with a very irregular seabed and soil composition ranging from stiff to soft clay. The gas reserves cover a geographical area of approximately 350 km2, approximately 40 km long and up to 8-10 km width. The design capacity is 1,750 MMscfd. Two base cases have been considered by the stake holders. One base case is a Tension Leg Platform (TLP) in deep water. The other base case is a complete subsea field development based on wet gas evacuation to shore (Subsea to Beach). A major challenge for both base cases is the liquid hold-up and terrain slugging induced by the heavily undulated seabed. For the Subsea to Beach option, this risk also applies to the whole 150 km tie-back to shore and will be significantly more severe. During shut-in of the 30’’ flowline infrastructure, liquids may flow back and accumulate in the deep water section of the pipeline. The back pressure on the wells induced by the hydrostatic head of the liquid column will severely complicate start-up. Liquid hold-up and slug management will necessitate: extensive seabed correction (rock dump) •
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frequent pigging strict operational turn-down limitations and • ramp-up procedures costly slug catching facilities on the beach and on the • future compression platform Twister subsea gas processing would ensure dry, single phase gas export enabling tie-back to a fixed platform in shallow water (SWP). The subsea Twister template conditions the gas to sales specification, ensuring dry, single phase export, preventing flow assurance issues such as corrosion, hydrate formation and slugging. Considering the tight gas specifications (Water dewpoint -18ºC at 69 barg and hydrocarbon dewpoint -10ºC at any pressure above 50 barg), seawater cooling to 5-10ºC will be needed upstream of the Twister module. Glycol (MEG) injection will be required to prevent hydrate formation. The gas is exported through two 30” (maximum line size for deep water installation) pipelines to a fixed platform in shallow water for compression and export through a single 42” CS pipeline. The liquids (condensate & rich MEG) are produced back free-flow to the shallow water platform through a separate 8” flowline. The condensates are stabilised and stored in the concrete storage cells of the fixed concrete platform with an off-take facility for shuttle tankers. The MEG is regenerated, evaporating all produced water and eliminating the requirement for water disposal. Power (mainly for the seawater pump) and controls are supplied to the Twister subsea templates from the shallow water platform. Lean MEG can be supplied back through the control umbilical or dedicated MEG return line. •
T LP
F SU S hu tt le
a) Tension Leg Platform
Shuttle Onshore plant
b) Subsea to Beach
SWP Shuttle
c) Subsea Twister Figure 10 - Case study of deep water gas field development options
A comparison between the two base case options and the subsea Twister option indicates estimated savings of US$300 million for the surface facilities. The main savings of the subsea Twister template tied-back to a SWP versus the TLP in deep water are summarized below: Substructure: The cost of a fixed concrete structure in • shallow water is significantly lower compared to a TLP. Topside: The costly turbo-expansion facilities with • associated utilities and manning can be avoided. Condensate storage: A dedicated FSU can be avoided by • integrating concrete storage cells in the substructure design. Risers: Flexible, dynamic risers can be avoided. The • concrete substructure can accommodate cost effective JTube pull-ins of rigid flowlines, export lines and umbilicals. Seabed correction (rock dump): dry, single phase • pipelines will require significantly less seabed correction since no terrain slugging will occur. The results of the feasibility study have been reported and distributed to potential end-users to gain support for a second phase subsea pilot project. The scope and planning of such a project indicates that development and pilot testing of the necessary technology will take an estimated four years, provided that support for an actual pilot project can be obtained.
Conclusion Twister is an innovative gas conditioning technology with some distinct benefits compared to conventional technologies. Although a relatively new technology, extensive operating experience has been obtained with commercial scale test units in five different gas plants in the Netherlands since 1998, in Nigeria since 2000 and in Norway since 2002. These test units have proven the viability of gas conditioning to typical pipeline specifications as well as the practicality of unmanned operation. The first commercial Twister application will start operation during the fourth quarter of 2003 on the B11 platform offshore Malaysia. This will be an important milestone in obtaining industry acceptance for this new technology. Second generation Twister technology will be field tested early in 2004, promising a step change performance improvement and reduced pressure drop. Twister combines dehydration and dewpointing, enabling dry, single-phase export, eliminating many flow assurance risks and limitations associated with wet, multi-phase export systems. High level economic screening indicates that Twister can be a highly competitive development option. The optimum concept for each specific gas development will obviously depend on many parameters including capacity, water depth, distance to market and corrosivity. Twister technology is simple and reliable and therefore widely recognised as the missing link for subsea gas processing and a key enabling technology for the development of currently uneconomical gas reserves. A feasibility study
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revealed no show stoppers. Case studies have confirmed the benefits and potential savings. Further information and contact details are available on www.TwisterBV.com.
Acknowledgement The achievements presented in this paper would not have been possible without the valuable input and support from many parties, most notably NAM, SPDC, SSB, FMC Kongsberg, Norske Shell, Shell Technology Norway and Demo2000.
References 1. Okimoto, F.T., Brouwer, J.M.: Twister Supersonic Gas Conditioning – Studies, Applications and results, GPA paper, San Antonio (2003). 2. Twister BV, FMC Kongsberg Subsea AS: Demonstration of Twister for subsea application , REP-0000021304 (2002).
Abbreviations TEG = Tri-Ethylene Glycol MEG = Mono-Ethylene Glycol CRA = Corrosion Resistant Alloy CS = Carbon Steel LTX = Low Temperature Separator with heating coils GGHEX = Gas/Gas Heat Exchanger CAPEX = Capital Expensiture OPEX = Operating Expenditure TLP = Tension Leg Platform FSU = Floating Storage Unit ppm = Parts per million
Table 1 - Cost comparison for offshore gas development options
Capital Expenditure (Surface) 1,000MMSCFD 100m waterdepth
TEG
Platform
185
120
Pipelines (100km)
45
Slugcatcher
35
Onshore treatment Total US$MM (%)
Wet Gas Wet Gas CRA CS
Scope
Twister
TEG
Wet Gas CRA
Wet Gas CS
Twister
120
165
Manned
Unmanned
Unmanned
Unmanned
120
50
35
3x24" CS
3x24" CRA 6" CS
3x24" CS 6" CS
48"CS 12" CS
35
35
-
Yes
Yes
Yes
No
50
55
55
35
Gas/Liquid treatment
315
330
260
235
(121%)
Gas/Liquid Gas/Liquid treatment, treatment, MEG regen. MEG regen. (127%)
(100%)
Liquid treatment (90%)
