Revamping of a Conventional Total Recycle Urea Plant
Mr. Narayansamy Selvaraj Head of Urea -1 Plant - QAFCO Qatar
Revamping of a Conventional Total Recycle Plant
by N. Selvaraj, QAFCO, Mesaieed, Qatar
Prepared for Presentation at 24th AFA Int’l Technical Fertilizers Conference 22-24th November 2011, Amman, Jordan
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Recently Qatar Fertilizer Company, Urea Casale and Qatar Constructions Company (QCon) have successfully carried out major Urea revamp project by applying Urea Casales’s technologies. This paper gives an overview of a project recently completed, which involved the application of the above mentioned technologies.
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FOREWORD A significant and recently accomplished example of urea revamping project aimed at fulfilling large capacity increase with Melamine off gases integration is: - The Toyo Total Recycle Urea plant revamping of Mesaieed (Qatar) plant (start up June 09) in connection with the installation of the new Eurotecnica Melamine plant.
This project represents a very important example of innovative technology for large scale revamping project applied to urea plants originally designed with a total recycle technology largely utilized in the world.
INTRODUCTION In July 2007 UREA CASALE (UCSA) and Qatar Fertilizer Company (QAFCO) signed a Contract for the revamping of the Total Recycle urea plant (Toyo technology) located in Mesaieed (Qatar). The original capacity of QAFCO Urea plant No1 was 1,000 MTD; the plant used to run, before revamping, at the overall capacity of about 1,320 MTD. The scope of the project was to integrate the existing urea plant with a 60,000 T/y melamine plant designed with Eurotecnica technology. The revamping was aimed at increasing the urea synthesis capacity up to 1,610 MTD (about +30%). The increase in plant capacity was achieved by utilizing the recycle Carbamate from the Melamine plant. Beside the Melamine integration, the other major objective of the Urea-1 revamp project was environmental improvement to eliminate the ammonia and urea emissions from the Urea-1 plant to the sea.
Proposed Technical Solution From process point of view, the main disadvantage of urea-melamine plant integration is the surplus of Carbamate flow recycled back to the urea synthesis loop (about +50% compared to the figures of a stand-alone plant), which has a detrimental impact on the reactor conversion. CASALE opted for revamping the synthesis unit with its High Efficiency Combined (HEC) process, thus providing a technology able to improve the overall CO2 conversion and minimize the modifications in the downstream sections. In addition the project provided the implementation of a new process condensate treatment unit, designed according to CASALE HEH (High Efficiency Hydrolyser) technology, in order to produce BFW quality treated condensate A process block diagram of the overall urea plant is illustrated in figure 1.
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NEW OFF-GAS CONDENSATION SECTION
CARBAMATE
CARBAMATE
NH3
OFF GAS
L.P. RECYCLE
M.P. RECYCLE
AMMONIA RECOVERY
PURIFIED CONDENSATE WWT
PROCESS COND. CARBAMATE NH3
CO2 + INERTS
OFF GAS
M.P. DECOMPOSITION
UREA SYNTHESIS UREA SOLUTION
OFF GAS
L.P. DECOMPOSITION DECOMPOSITION
PROCESS CONDENSATE
UREA FINISHING
EVAPORATION
UREA SOLUTION
UREA PRODUCT
UREA SOLUTION UREA SOLUTION
MELAMINE MELAMINE UNIT PLANT
NEW / MODIFIED SECTION EQUIPMENT IN MELAMINE PLANT
MELAMINE
Fig. 1 - Urea Total Recycle Plant integrated with Eurotecnica Melamine The main modifications were the ones relevant to the synthesis loop:
New secondary reactor equipped with high efficiency trays New stripper New Carbamate condenser New Centrifugal Carbamate pumps (replacement of existing Reciprocating pumps)
Apart from the pure process aspect of providing additional surfaces, additional reaction volume in synthesis as well as pumping capacities, the main constrains of the project were the limited space and the reduced shut-down time available to implement the new installations. CASALE selected to adopt a different approach aimed at improving the synthesis efficiency up to a level where the downstream section would not be significantly affected by the integration with the Melamine plant.
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The modification of the synthesis loop is shown in figure 2. In figure 2a is shown a picture for the new HEC loop.
INERTS
STEAM
COND. STEAM
COND. CARBAMATE
UREA SOLUTION
CO 2
NH 3
NEW EQUIPMENTS
Fig. 2 - New HEC Loop of Total Recycle Urea Plant In order to improve the synthesis loop efficiency CASALE adopted the HEC technology introducing a Secondary Reactor, with the relevant Stripper used as reboiler and using the existing primary reactor with once through configuration together with the new Carbamate condenser. The modification led to the fundamental results of obtaining a higher conversion of the loop even if under a drastically worst H2O/CO2 ratio. In fact the loop before revamp was running with 0.57 H2O/CO2 ratio (as per original material balance) and the conversion of 64% while with melamine integration the H2O/CO2 ratio has raised to 0.93, but thanks to the installation of HEC the conversion of the loop has increased to more than 70%. The result of this modification is that the medium and low pressure sections do not include significant modifications and the new added HP section can be easily and quickly tied in, thus limiting to the maximum extent the shut down period.
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In fact the plant was started up in June 2009 after a shut-down of only 26 days urea to urea. The Urea plant has been operated without Melamine integration up to May 2010 since the Melamine project was ready only at that time. At present the plant is running full capacity integrated with Melamine unit running at full load from middle December 2010.
Fig. 2a - New HEC Loop picture
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In addition to the HEC Loop, a new off-gas condensation section was added consisting of L.P. Carbamate pumps (located in the Urea plant), Off-gas condenser with relevant tempered cooling water system and Carbamate recovery tank (located in Melamine plant). For this section UC supplied the Basic Engineering Design package. Detailed Engineering and procurement for this section was done by Eurotecnica. The scheme of off-gas condensation is illustrated in figure 3.
INERTS
OFF GAS
CARBAMATE FROM L.P. RECYCLE
M. P. RECYCLE SECTION
C.W .
CARBAMATE TO H.P. SECTION
Fig. 3 - New Off-gas Condensation Section
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Besides the Melamine integration the project foresaw the replacement of crystallization with evaporation section and the provision of a brand new Waste Water Treatment (WWT) section of capacity 65 MT/h, to eliminate Ammonia and Urea going to the sea. In the enclosed figure 4 we show a process flow diagram of the new Waste Water Treatment sections. In figure 5 we show a picture for the new Desorber / Hydrolizer columns.
Fig. 4 - New Waste Water Treatment Section
The WWT design is based on CASALE HEH (High Efficiency Hydrolyser) technology; the operating pressure of the hydrolyser (using MP steam) is about 20 bar. Since the first operation, the new WWT section has demonstrated to be to produce treated condensate suitable for BFW use (after passing through a polishing unit). In fact the ammonia content in the treated condensate has been detected to be approximately 2 ppm while urea is less than 1 ppm.
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Installation of the unit completely eliminated the ammonia and urea emissions to the sea from Urea-1 plant, thus meeting the commitment given to the environmental authorities.
Fig. 5 - New Desorber / Hydroliser Columns picture
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Plant Operation For your reference, please find in the attached table some operating data of the plant before and after melamine integration.
Parameters Synthesis capacity NH3 consumption CO2 consumption Steam consumption Sea Water consumption (dT=7째C) Electrical consumption Carbamate recycle Specific carbamate recycle Total Off-Gas flow NH3 in Off-Gas CO2 in Off-Gas H2O in Off-Gas NH3/CO2 loop ratio H2O/CO2 loop ratio Overall loop conversion
Unit [MTD] [kg/ton of U] [kg/ton of U] [ [Gcal/ton of U] [m3/ton of U] [KWh] [kg/h] [kg/ton of U] [ton/h] [ton/h] [ton/h] [ton/h] [%]
Before revamping
Current with Melamine off gas
1,320 580 752 67,000 1,237 -
1,680 568 740 0.88 135 105,000 1,509 About 30 About 13.5 About 10 Balance 3.58 0.93 72
3.48 0.57 64
Remarks
As it is clear from the above table, the introduction of the HEC CASALE technology enables the increase of HP loop capacity thanks to the improvement of the synthesis efficiency. The specific Carbamate recycle flow has increased by 20% only despite the Carbamate flow increased of about +50%, which is a further confirmation of the improved efficiency of the system.
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Project Execution After a feasibility study, QAFCO and Urea Casale agreed to enter in a Contract for the execution of the project. Urea Casale’s scope of work covered:
Basic Engineering Detail Engineering Supply of all Equipment and Materials Site Assistance during construction Site Supervision during commissioning, start-up and test-run.
Construction was performed by a local company (Qatar Construction Company) directly hired by QAFCO. Since the initial phase of the project, QACFO nominated a project team to follow the project, which, during the engineering phase, was located in Urea Casale offices. This approach gave the advantage to simplify and speed-up communications and contingency plans implementation. The engineering activities performed by Urea Casale covered also the complete HSE – Health, Safety and Environment analysis (HAZOP, SIL, Risk and Noise analysis, etc.) of the revamped plant during Engineering phase of the project, which are required to satisfy the very stringent local norms and standards.
Project Main Milestones
Effective Date of Contract: 1st September 2006 Shutdown of Urea-1 for final revamp activities: 24th May 2009 Restart of Urea-1 after shutdown: 19th June 2009 (total plant shut-down only 26 days urea to urea) Urea-1 & Melamine integration: from May 2010 (Melamine plant was ready only at that time). Performance Test of Evaporation section: 14-15th April 2010 Urea-1 at 100% capacity, integrated with melamine plant: mid Dec 2010 (Melamine plant reached 100% load only at that time) Urea-1 Plant performance test, integrated with Melamine plant at 100% load: June 2011.
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Project Execution Challenges The execution of the project posed many challenges to the Company and the contractors, some of which are listed below:
The contract strategy of Engineering and Procurement with Urea Casale and Construction with Qcon, led to many coordination challenges to the Company, due to lack of experience with such contract strategy. The project required nearly 450 tie ins. To execute such large number of Tie ins, majority of which were done in a running plant or during unplanned short stops were difficult to execute. Major part (around 80%) of the construction was done in a running plant. This required the presence of large number of construction workers presence in the plant, which posed safety challenges. While routing the new pipelines, there were many clashes with existing pipelines, both with above ground and underground pipelines. Making new pilings for installing new equipment/structure very close to existing equipments in a crowded, running plant was a difficult task. Training of the operators, to adapt to the new process, was difficult. Training has to be done while the plant is online and the change from old process to new process happens too quickly after the final shutdown.
Conclusion The Urea-1 revamp was a successful project, having met all its project objectives, without any safety or environmental incidents. This was achieved through the dedicated team work of all involved personnel from QAFCO, CASALE and QCon.
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