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1 Acid treatment upgrade for Qatar Upgrading acid treatment at the world s largest LNG facility safeguards the plant s design capacity and its ability to process increasingly sour feeds GAUTHIER PERDU, LAURENT NORMAND and GERALDINE LABORIE Prosernat OMAR ALHATOU Qatar Qatar is the world s largest liquefied natural (LNG) company. It annually produces and supplies the globe with 42 million tonnes of LNG from its four ventures (Qatar 1-4). A joint venture of Qatar Petroleum, ExxonMobil, Total, Mitsui and Marubeni, the company has headquarters in Doha, Qatar and maintains its upstream assets in Ras Laffan. Natural is supplied to Qatar s LNG trains from the massive North Field, by far the world s largest non-associated field. Together with RasGas, the company achieves LNG production of 77 million t/y. The company was originally formed to operate three LNG trains with a design capacity of 2 million t/y each. Then, Qatar 1 was upgraded in 2005 through a debottlenecking project, which resulted in a new capacity of 10 million t/y. Plateau Maintenance Project The recent completion of the Plateau Maintenance Project (PMP) ensures that the production capacity of Qatar 1 is maintained at 10 million t/y of LNG for many years to come. This has been accomplished by drilling additional offshore wells, modifying associated offshore facilities, modifying the existing Qatar 1 Trains 1, 2 and 3, and adding onshore facilities to accommodate expected increases of hydrogen sulphide ( ) and carbon dioxide (CO 2 ) contents in the feed. With these new sources, the and CO 2 content would be above the maximum levels that can be handled by the existing facilities to keep production of LNG at maximum flow. Additionally, the content of and CO 2 will not be stable over time, but is expected to rise according to the wells in production. Contents can even be adjustable, but they will definitively stay above the and CO 2 levels the original plant was designed for. The existing pretreatment units of Qatar 1 LNG plant consist of three parallel ulphinol D units, designed by hell and capable of handling a with 0.9% and 2.4% CO 2. The acid produced by the ulphinol plant is sent to an existing 634 t/d sulphur production plant. The ulphinol units accommodate the presence of mercaptans in the feed, with the support of polishing units installed downstream. The additional quantities of are treated in new onshore facilities composed of a new acid removal unit (AGRU) and a new sulphur recovery unit (RU), as part of the project. The new plant is based on a single train concept and is capable of treating over 1.1 billion cubic feet per day (bcfd) of offshore feed, located upstream the existing LNG trains. The basic principle is to remove the extra amounts of and CO 2 from sourer feed, down to levels acceptable to the existing downstream facilities. The acid from this new AGRU is sent directly to a new dedicated conversion unit in order to produce sulphur and meet emission standards. Numerous new or upgraded compression and utility units were also included as the onshore project had a major brownfield component, with the scope of work conducted Gas

2 Raw Treated to ulfinol Unit 1100 MMCFD HP absorption Rich amine Flash to fuel system MP flash HV Preflash column Lean solvent within the existing operating facilities and equipment. After Chiyoda and Technip had carried out early conceptual studies in 2004 and 2005, followed by the feasibility study, pre-front end engineering design (pre-feed) and FEED of the facilities from 2006 to 2008, the Technip-Chiyoda joint venture (TCJV) was awarded the engineering procurement and construction (EPC) contract by Qatar for the onshore work of the project in Technology selection for the licensors of a new AGRU and sulphur plant was carried out in Based on its preflash low BTX process, within the AdvAmine technology portfolio, Prosernat was initially appointed to supply the design of the new selective AGRU, while the sulphur plant is based on a technology supplied by another company. The initial phase had considered two parallel 600 million scfd AGRU + RU/TGTU trains within a separate plot area dedicated to AGRUs, another dedicated to RU/ TGTUs, and a third for solvent Prosernat AGR No.4 and TGT No. 4 units Flash Acid Regenerator RU Licensor RU + incinerator RU + (KTI pa) Tail Lean solvent Incinerator emi-lean solvent recycle Tail Figure 1 Gas treatment unit of the PMP project: arrangement of AGRU + RU TGT storage tanks. For that phase, there was already a constraint in available space within the existing LNG trains, congested after the 2005 debottlenecking phase. The initial scheme had resulted in stretching the distance between the AGRU and the RU of each train. The project eventually went to a fast track review FEED in Qatar decided that more space constraints could be solved by a single train, with additional and significant benefits on project costs. Qatar therefore considered a single train of 1.1 bcfd with integrated AGRU + RU + TGTU, installed within a single plot area. Optimisation has also been achieved thanks to a patented design proposed by Prosernat, in which all the amine units and sections of the plant (low BTX AGRU + acid enrichment + amine section of the TGTU + common regeneration) are fully integrated. The available area allocated for the greenfield part of the project was a single 365 x 150 m zone, already occupied by approximately 100 x 150 m of existing instrumentation and HVAC facilities. One of the most impressive achievements of the project has been the installation of one 1.1 bcfd treatment plant plus 880 t/d sulphur, tail and incinerator units within m 2. The storage tank area was left at the initial location. The project was completed in 2014 and the plants went into operation in eptember The feed flow of was quickly and successfully raised to the design capacity. The new plant satisfactorily passed performance checks and reception was at the beginning of The PMP project also hit records in term of HE management since the project team, along with their contractors, worked over 42 million man-hours in a very difficult operating environment, achieving world class safety performance, including an exceptional total recordable incident rate (TRIR) of 0.23 for every hours worked. More importantly for Qatar, the project met the objectives of the company in term of its safety incident and injury free culture, particularly in the application of the TOP safety observation programme, where a peak workforce of 6500 completed over observation cards, which helped identify and mitigate safety risks. Design of the new treatment unit The selected process scheme for the new AGRU is the preflash low BTX (see Figure 1). It includes a low pressure preflash of rich MDEA solvent 2 Gas

3 in a dedicated column installed upstream the MDEA regenerator, with routing of the recovered to the TGT. The possibility to recycle a part of the acid from the regenerator overhead to the preflash column for an enrichment step was also implemented for leaner feed cases (containing 1 mol% ) and for the turndown case. The proposed scheme is based on AdvAmine technology. It gives additional flexibility in terms of composition range and also efficient operating adjustment. Acid feeds the RU, followed by a and quench section for tail. The tail from the TGT goes to an incinerator, installed close to the new units. The plant also takes advantage of the integration of a high pressure and tail. emi-lean solvent from the TGT is recycled to the high pressure after mixing with fresh lean solvent from regeneration. The scope of Prosernat as AdvAmine process licensor covered the design of the complete amine unit, including the AGRU s high pressure, the preflash column, the TGT and the solvent regenerator. Due to the highly integrated amine, RU process configuration, heat and material balances were prepared by iterative calculations between Prosernat and the RU licensor. our feed The new treatment unit allows for four design and operating cases. There is a Case Feed composition Feed, Feed Acid CO 2 content, content, flow rate, temperature, content to % mole % mole MMscfd C RU, % mole dry basis dry basis Design P90 ummer Design P90 ummer Normal P50 Winter Turndown Table 1 Operating cases of the new treatment plant Case Design case Normal case Turndown case Composition case P90 ummer 2021 P50 Winter % mol Composition ppmv ppmv ppmv CycloC Aromatics CO Mercaptans Table 2 single design for the AGRU, but this design covers the complete range of feed flow rates and compositions shown in Table 1. The feed pressure for all cases is 73.8 bara. The new plant was allocated only a 1.0 bar pressure drop between the inlet and outlet battery limits. The feed includes mercaptans, CO and aromatics, which the new unit has to accommodate. These are detailed in Table 2. Gas specifications Treated The new treatment plant has to produce an acid with a maximum of 600 ppmv and 1.8% vol CO 2, at 50 C. Acid The acid from the solvent regeneration system is supplied to the downstream sulphur plant in respect of the following specifications: 1.15 barg at Contaminants present in the feed the inlet RU knockout drum, at a temperature of 45 C and with 54% mol minimum wet basis. Operating cases at 60% in the acid were also requested by Qatar. Flash The flash produced by the flash vessel has to meet a 50 ppmv specification at 7 barg. Tail The TGT treated from the TGT has to contain 250 ppmv (wet basis) maximum at near atmospheric pressure to feed the incinerator. ulphur plant and incinerator The capacity of the RU is 874 t/d of sulphur for the maximum design case. Turndown capacity is 235 t/d of sulphur. The sulphur recovery efficiency is 99.25% of the total sulphur contained in the Gas

4 sulphur feed. The design of the sulphur plant accommodates a maximum of 500 ppmv aromatics and 500 ppmv mercaptans in the acid. The rundown of bright yellow sulphur complies with the following main specification: Purity (dry basis) wt%: 99.8 wt% plus x 350 ppmwt Organic matter as carbon 400 ppmwt Ash 200 ppmwt Acidity (as O 4 ) 50 ppmwt No dark particles. Incinerator specifications are: plus CO plus C 2 50 mg/nm 2% vol O 2 Carbon monoxide 5000 mg/ Nm 2% vol O 2 BTX plus C 6 + conversion in % 99.9 Base case When the project went to selection of licensed technologies at the end of 2005, Qatar was looking for a single technology licensor for sweetening (including potential enrichment of the acid upstream the RU) and for the TGT. The latter was to include plus quench of the tail, followed by an. Qatar went to a separate bid for the AGRU/ TGTU and the RU/ and quench sections. The technology specified for sweetening was to be an amine based technology. The need for a selective AGRU technology was obvious and MDEA processes were proposed. However, the quality of acid sent to the RU contains in some cases less than 50%, contaminated by aromatics and mercaptans. These are potentially harmful to efficient operation of the RU unit. Therefore, the question of enrichment of the was raised. Optimisation of the needs of the new units in terms of utilities and installation area was also carefully considered since the new installations were to be built within one existing plant. team and cooling water supplies available in the existing facilities might be limited. However, Qatar could expect to minimise the debottlenecking works at the centralised utilities generation plant if new demands made of it were moderate. Basically, the need to handle the various cases in two trains of 800 million scfd design capacity the initial configuration of the project after the conceptual study, where the normal flow rate to the trains was to be 600 million scfd with a design capacity set at 800 million scfd required a 540 m 3 /h amine based high pressure AGRU and a 240 m 3 /h TGTU per train. The corresponding reboiling duties could be estimated at 39 MW for the AGRU and 16 MW for the TGTU at regeneration. Prosernat bid with a first configuration in which the rich solvent of both the AGRU and the TGT were regenerated commonly in a single column, and the solvent from the TGT, partially loaded with and CO 2, was reused in the AGRU s high pressure. The arrangement gave significant savings compared to a solution with two separate units, since the total solvent flow rate was eventually 600 m 3 /h and the reboiler duty was only 48 MW. The process configuration is shown in Figure 2. For this configuration, the acid loading is 0.67 mole of acid per mole of amine in solvent. The solvent loading is no higher than in MDEA sweetening plants based on AdvAmine technology in operation for many years in similar ambient conditions in UAE. The acid produced by the design case has 53% mol wet basis, and approximately 1200 ppmv aromatics and mercaptans. Although the basis of the design of the RU had not put restrictions on the BTX content for the bid evaluation of RU licensors, it appeared that the content of aromatics in the acid became an issue for the design of the RU. Even for lean cases, the high pressure AGRU delivers acid with less than 45% mol, but still with ppmv aromatics. The configuration of the RU had to be adapted to handle such feed es, and has to rely on more complex technologies to design the Claus thermal stage. Technologies such as co-firing with fuel or enrichment of air with oxygen were not required by Qatar. Quality of the acid charge of the RU The problem with the quality of acid is the aromatic content (1200 ppmv) associated with a low content of (45-53%). The content is insufficient to cause full oxidation of these aromatics in the thermal stage of the sulphur plant. Remedies can focus on two fronts: 4 Gas

5 Treated Acid RU + + quench HP AGRU Feed Fuel AGRU + TGTU common regenerator TGTU Figure 2 Initial configuration proposed by Prosernat for the AGRU Reducing aromatics in the acid Increasing the content of in the acid to allow complete oxidation of the aromatics at the thermal stage of the Claus unit (generally above 1050 C). Reducing aromatics in acid Known industrial solutions can involve treating the acid on activated carbon beds for adsorption of hydrocarbons. This technology has been developed by audi Aramco and has been widely used in audi Arabian plants. It seems to have some drawbacks: the effectiveness of activated carbon is better for light aromatics (benzene), and there is a need to regenerate the beds periodically. Finally, the size of the beds themselves is very large. In the PMP case, the quantity of aromatics approached 3.6 t/d in the acid. The space constraints of the project could not permit such a configuration. Another approach would be to process the acid in an additional low pressure MDEA unit, which would solve the issue twice: by first strongly decreasing the aromatic content of the rich (the partial pressure of these compounds is considerably lower than in the raw, to limit absorption by MDEA); and secondly, by selectively absorbing but slipping CO 2, to produce a enriched with at the regenerator. The major drawback would be the cost of this second wash (another selective amine unit almost as expensive as a high pressure AGRU). There would be also an additional loss of sulphur in the CO 2 released to the incinerator since the concept adds one supplementary. Eventually, Qatar wanted to study the enrichment of acid to increase the content of and reduce the content of mercaptans and aromatics. In this case, the integrated amine high pressure and TGT s in one common regenerator already proposed by Prosernat delivers a situation conducive to less costly solutions: Integrating enrichment to the TGTU with a dedicated Improving the selectivity of the high pressure sweetening unit upwards to a quality that allows complete oxidation of aromatics at the thermal stage of the Claus unit, using Prosernat s preflash low BTX process. Integrating an enrichment in the TGTU The bulk specification requested in the treated (600 ppmv) enables the valorisation of semi-lean amine from the TGT for reuse in the high pressure. The benefit is still seen if an acid enrichment is installed, despite increased Gas

6 Treated RU + + quench HP AGRU AGRU + TGTU common regenerator Feed Fuel TGTU AGEU Figure 3 Enrichment by integration of the acid in the TGTU loadings of acid in the solvent. It is even possible to consider two low pressure s installed in series, so that the problem of increased rejection of to the incinerator is mitigated. The scheme is shown in Figure 3. A fraction of the acid produced by the regenerator is washed in a dedicated (which can be the lower part of a stacked TGT in a patented process) installed close to the of the TGTU. The gain is the use of the remaining absorption capacity in the semilean amine flowing from the TGT after the tail is cleaned up. The purpose of this operation is to partially enrich the acid and slip the aromatics contained in the fraction of acid. The effectiveness of the operation is directly related to the amount of acid that is recycled, at increasing cost. Furthermore, rich amine from the bottom of the AGRU is much more concentrated than the one coming from the TGTU. Its use in the high pressure can become problematic. It is then necessary to increase the flow of fresh solvent. AdvAmine preflash low BTX process The configuration shown in Figure 4 adds a supplementary low pressure flash tower upstream the regenerator to flash the rich solvent after preheating. The vapour produced is recycled to the TGT, while the rich amine liquid solvent is routed to the head of the regenerator. The arrangement had been already implemented by Total in the 1980s when the company operated selective MDEA plants in the plant at Lacq, France. The advantages of this new system are multiple: Firstly, the low pressure flash of a rich amine solvent preferentially vaporises CO 2, which is a simple way to enrich the rich solvent in, then the acid from the regenerator. econdly the flash of the rich amine solvent also releases a large fraction of aromatics, which is sent into the of the TGTU, then evacuated to the incinerator. The efficiency of this arrangement is far greater than the 6 Gas

7 Treated Pre-flash tower RU + + quench HP AGRU Feed Fuel AGRU + TGTU common regenerator TGTU Figure 4 Preflash low BTX process with integration of semi-lean solvent from the TGTU efficiency of recycling acid, mainly because the concentration of in the flash is significantly lower than in acid. The semi-lean solvent from the TGTU is then less concentrated in and more useable in the high pressure to spare the use of fresh amine. The operating pressure of the preflash column is adjustable by operators, to control the enrichment power of recirculation in respect of the composition and flow of sour feed to the high pressure AGRU. The lower the operating pressure of the preflash column, the higher the content of in acid to the RU. At PMP, the configuration is available to adjust the concentration of acid between 54% mol (when the operating pressure of the preflash column is 4 barg) to 60% mol or more, at lower operating pressures. Despite higher recirculation flows of low pressure flash, and therefore more acid in semi-lean solvent from the TGTU tower, the 600 ppmv content requested at the top of the high pressure still allows recycling of significant amounts of semi-lean solvent, without risking the specification. The arrangement saves substantially on reboiling duties. Comparison of performances between the schemes The performances of each process were evaluated and the results were proposed to Qatar. A comparison for the 800 million scfd design case is shown in Table 3. Based on these results, the AdvAmine preflash low BTX process proposed by Prosernat was finally selected by Qatar for the project. At the more detailed optimisation phase at the beginning of the FEED phase, Prosernat considered the addition of a specific recycle of hot acid from the top of the regenerator to the preflash tower via a dedicated line. The scheme, based on solutions patented by Total when it operated the Lacq plant, improves more significantly the quality of acid. It acts as a superenrichment process configuration in the worst conditions. This option allows more to be sent to the TGTU and is operated only when the unit has extra quantities of fresh solvent available from the regenerator in turndown conditions. The Gas

8 Treated Pre-flash tower Acid recycle RU + + quench HP AGRU Feed Fuel AGRU + TGTU common regenerator TGTU Figure 5 Preflash low BTX process with acid recycle to TGTU pressure of the preflash tower needs to be below that of the regenerator top to circulate acid. For PMP, the connection is activated only for turndown 1% and start-up cases. Figure 5 details the arrangement. Description of the acid treatment unit A process scheme of the acid treatment unit is shown in Figure 6. In the high pressure section, the raw feed is first filtered then contacted with an amine solvent that is a mix of a very lean solvent and semi-lean amine solvent already used in the TGT. The fraction of each amine solvent can be adjusted to be as close as possible to the required specification, and the number of trays in the is adjustable to control CO 2 slippage. The treated is cooled through a vertical direct cooler, operating with a closed cooling water loop, to limit the pressure drop of the high pressure section. It also enables water wash of the solvent to limit solvent losses to downstream units. The rich amine recovered at the bottom of the MDEA is released at 7 barg through a level control valve. The flash is treated with a slipstream of lean amine in a dedicated stacked on the medium pressure flash drum. The rich solvent is then pre-heated with the lean solvent from the bottom of the regenerator through the rich/ lean MDEA exchangers. The hot rich solvent then feeds the preflash column at reduced pressure. The flash of the rich solvent releases some of the acid es, mostly CO 2, and hydrocarbons. The operating pressure is adjustable. It controls the differential ratio of released CO 2 to. The recovered at the top of the preflash column is cooled and reflux water is sent back to the column. The flash is mixed with the tail from the RU section and feeds the TGT, where it is contacted with fresh solvent from the regenerator to 8 Gas

9 Treated AGRU pre-flash tower Acid recycle RU + + quench ulphur HP AGRU Fuel AGRU regenerator Feed Reboilers TGTU LP steam Figure 6 Flow scheme of the acid treatment plant, including AGRU, RU and TGTU achieve specification. The rich amine from the preflash column is sent to the regenerator where and CO 2 are stripped by the vapour generated in the reboiler. The top of the regenerator is equipped with a direct condensing section where acid is cooled by a flow of water circulating in a closed loop. This arrangement maximises the available pressure of the acid at the AGRU s battery limit. It was set at the FEED stage to limit the footprint and diameter of the acid headers to the RU, with higher allowable pressure drop. The new AGRU is equipped with an acid line that allows recycling of acid Design challenges Beyond the elaborated multicolumn process scheme, the project has been a great chalfrom the top of the regenerator to the preflash column. This facility is used to meet the minimum content of the acid even when the feed contains only 1% of. The line can also be used during turndown conditions. The lean solvent from the bottom of the MDEA regenerator is cooled in the rich/lean MDEA exchangers. Air cooling and water cool the solvent. Cooled lean amine solvent feeds the high pressure, the medium pressure and the TGT. Filtration is achieved with cartridges filters installed on a side stream of the lean solvent loop. The semi-lean solvent from the TGT is also filtered before recycling to the lean solvent loop. Depending on the feed composition ( /CO 2 ratio and feed flow), the operating conditions of the AGRU are adjusted to achieve the required specifications, especially the concentration of in acid. Two parameters are essential and specific to the good operation of the unit: the recycle rate of semi-lean amine in the solvent feed to the high pressure ; and the operating pressure of the preflash column. Gas

10 lenge in terms of the design and concept of mega-sized equipment: The high pressure AGRU fitted with trays has an inside diameter of more than 6.5 m and is one of the largest high pressure columns amongst AdvAmine references. Close attention has been paid to optimisation of the tower size and to the design of the trays. The AGRU regenerator has an inside diameter of 9 m at the bottom; its height is more than 41 m as the direct condenser is stacked vertically on top of it. This tower ranks as the biggest ever regenerator design using AdvAmine technology. The AGRU regenerator bottom has a buffer capacity as there is no surge tank installed in the solvent loop, but installed outside the AGRU s battery limit at some distance. The 1.1 bcfd AGRU is one of the largest for sour treatment in a single train amongst AdvAmine references. The start-up and the successful operation of plant tart-up chronology tart-up of the AGRU was Initial design Acid Preflash low recycle of TGTU enrichment BTX process solvent and common in TGTU regeneration Total amine flow, m 3 /hr Reboiler duty, MW content in acid, % mol wet BTX content in acid, ppmv wet concentration from HP AGRU, ppmv concentration from LP TGTU, ppmv Table 3 Comparison of three schemes in the initial FEED phase completed at the end of eptember 2014, and all new PMP units (AGR4 and RU4) were running in a smooth and stable way by mid- October First sulphur was produced on 10 October This article is based on a presentation to the International Petroleum Technology Conference, Doha, Qatar, 6-9 December 2015 and published with the permission of the ociety of Petroleum Engineers. Gauthier Perdu is Deputy VP Process and Application with Prosernat, in charge of technologies. He is an expert in the field of sweetening of natural es and disposal of acid es. He graduated from ENIGC Toulouse in 1995 as Dipl. Engineer and with a postgraduate certificate in chemical engineering. Laurent Normand is Business Development Manager with Prosernat, in charge of sales, licensing and technology development for treatment and CO 2 capture. He started his career at Lawrence Berkeley Laboratory (UA) and IFPEn (France). He holds a PhD from Ecole des Mines de Paris and graduated as an engineer from the engineering school of physics ENPG-INPG in France. Geraldine Laborie is an Amine Technologies Process Expert with Prosernat, in charge of basics development, amine unit detailed engineering, amine unit troubleshooting and upgrades with experience in amine unit start-up, operations and survey. he graduated as an engineer from the National Institute of Applied ciences (INA) of Toulouse, France. Omar Alhatou is a Process Engineering pecialist with Qatar. He holds a Bc degree in chemical engineering from the University of Jordan. 8 Gas