Authors:
A. ALVI, S. B. KUMAR
Tata Chemicals Ltd, Fertilizer Division
Babrala, India
Tata Chemicals Ltd’s Babrala unit operates an ammonia-urea complex based on NG/naphtha reforming. Haldor Topsøe of Denmark and Snamprogetti of Italy provided the process technology for ammonia and urea plants respectively. The focus on efficiency was right from the conceptual stages, which facilitated in selection of state of art technology. During the operation phase the focus was on process discipline, waste reduction / recycling and modifications for better reliability, safety and efficiency. With this approach Tata Chemicals could show continuous improvement in energy efficiency year after year and is a national benchmark in fertilizer industry and comparable with the best in the world. The equipment manufacturers and process licensors consider the facility as a reference plant.
A very important event for the operations group is the planned shut-down of the plant for annual turn-around. This can be a yearly activity or more in some cases, as per the requirements and the quantum of jobs accumulated. The success of these turn-arounds plays a critical part in the operating efficiency and reliability of operations, hence all care and expertise is required to execute them well.
In this paper we have tried to cover all the areas related to planning, preparation and execution of a safe and efficient annual turn-around. Basically here we are trying to give a picture of the same from the process side of operation. It broadly covers:
■ Shut-down job lists – Preparation, segregation, continuous updating and finalization
■ Estimation of duration of SD based on critical jobs
■ Materials and services planning
■ Safety preparedness and safety guidelines for service providers
■ Process planning – Preparation of “Shut-down Manual”
■ Preparation of shut-down reports, etc.
We have made processes and tried to standardize the entire process of annual turn- around planning and execution and have tremendously benefited from it. We are sure that sharing our experience with others in the industry will help them prepare better and in turn also help us to improve our processes and take us further in our journey towards excellence.
INTRODUCTION
The TATA group is a world-renowned group engaged in various sectors of national significance in India. The group operates in seven core sectors like Materials, Engineering, Energy, Chemicals, Consumer Products, Communication & Information System and Services. Tata Chemicals
Limited forms an integral part of chemicals group.
Tata Chemicals Limited, founded in 1939, comprises of three strategic business units – Chemicals,
Fertilizers, and Food Additive Business. The Chemical Division is a uniquely integrated inorganic chemical complex that produces various basic chemicals of which soda ash; cement and salt are the major products. TATACHEM holds a predominant position as a leader in the soda ash
industry. This inorganic chemical complex of TATACHEM is the largest not only in India, but also in this part of the world and ranks among the most self-reliant, energy-efficient and water efficient operations anywhere in the world.
The Fertilizer division consists of one Nitrogenous Fertilizer complex at Babrala and a Phosphatic
Fertilizer division at Haldia. The Babrala unit, started in December 1994, operates Ammonia – Urea complex based on NG/Naphtha reforming. The ammonia plant has an installed capacity of 1520 metric tonnes per day (MTPD) and is based on the low energy process of Haldor Topsoe A/S, and the urea plant consists of two streams, each having a capacity of 1310 MTPD based on the technology of Snamprogetti Spa, The related facilities of off-sites and utilities consist of a captive power and steam generation plant (CPSGP) with two gas turbines, two heat recovery units and one service boiler, cooling towers, demineralization plant, ammonia storage, naphtha storage, inert gas plant, effluent treatment plant, etc (Figure 1). The control system of the entire complex is based on TDC 3000 release 530 DCS of Honeywell. The operation of the plant is assisted by advanced process controller (APC) supplied by Honeywell Automation India limited. The company has installed an Enterprise wide Resource Planning (ERP) system SAP 4.6 C to monitor and integrate all key business operations across the organization for effective optimization and control.
The focus on efficiency was right from the conceptual stages, which facilitated in selection of state of art technology. During the operation phase the focus was on process discipline, waste reduction / recycling and modifications for better reliability, safety and efficiency. With this approach Tata Chemicals could show continuous improvement in energy efficiency year after year and is a national benchmark in fertilizer industry and comparable with the best in the world. The equipment manufacturers and process licensors consider the facility as a reference plant.
ANNUAL TURN-AROUNDS (ATR)
The ATR is one of the major activities at the complex from the point of view of planning and execution of all the major inspections, safety and maintenance. The shut-down of the plant is planned on an annual or a biannual basis depending upon the plant performance, jobs, inspections, or for fulfilling the statutory requirements like IBR inspection of boilers etc. Shut-down job list is prepared by all the concerned departments based on the recurring problems that can’t be resolved or attended in running plant, future plan based on the recommendation of the technology licensors, long term strategy plans, long term asset management plan and short term plan. Long-term asset management plan is prepared based on the life of the equipment, vendor input and the inputs from the regular conditional monitoring.
FIG. 1: PROCESS PLANTS IN THE COMPLEX
The success of these turn-arounds plays a critical part in the operating efficiency & reliability of operations, hence all care and expertise is required to execute them well. The maintenance functions like mechanical, civil, electrical and instrumentation are the main architects of the jobs but the responsibility of coordination of a safe and timely completion lies more with the operating departments.
In this paper we have tried to cover all the areas related to planning, preparation and execution of a safe and efficient annual turn-around from the eyes of operations people. Ammonia plant, being the most critical has been specially talked about in this document.
SHUT-DOWN JOB LISTS
Planning for next shut-down starts just after the completion of the previous turn-around with preparation of shut-down job list. Utmost care is taken in preparing shut down job list and it is updated throughout the year with the addition of jobs that cannot be done in the running plant. Apart from breakdown jobs it also contain critical equipment overhauling, internal inspections, modifications, catalyst change-out, internal cleaning (like exchanger tube cleaning) and preventive maintenance jobs.
To have clarity in planning the job list is divided into the following categories:
• Main maintenance jobs
• List of steam, oil and GV solution leakages
• List of gland leakages
• List of furmaniting jobs to be normalized
• List of clamps to be normalized
• List of burners to be repaired
• List of small valves to be repaired, etc.
Each job has its unique job number which helps in tracking its material, spares etc. The job list is reviewed on monthly basis by production & maintenance managers and sent to all service departments for procuring material and services related to each job. Shut-down job list is finalized based on the criticality of each job, the available time after meeting production targets, job that which is essential to run the plant efficiently for next two years, jobs that can be completed within that time. It is reviewed at senior management level regularly and responsibilities are assigned for each point. It helps us to prepare better in terms of material and people availability and align all the people and plan accordingly. Each and every job is identified & tagged well before the shut down.
ESTIMATION OF DURATION OF TURN-AROUND
The planning of all major jobs in the job list includes the time for handing it over for maintenance, maintenance time and the time to make it available for service. Inputs for optimum time requirement for these jobs are collected from ideas generated through brainstorming between production and maintenance functions at all levels and from internal as well as external benchmark timings available. Bar charts are prepared accordingly for all areas and all major jobs. The jobs requiring maximum time are identified as the jobs on the Critical Path. The time needed for these Critical path jobs is used to estimate the duration of Shut Down.
Plant people are regularly sent to other plants for benchmarking of their best practices. Based on these finding we have reduced our Ammonia plant cold start up time from 56 hrs to 36 hrs, primary reformer hand over to maintenance time and urea reactor cooling time. Experiences of other plants in duration of specific maintenance jobs are also taken into consideration for optimum utilization of time.
MATERIALS AND SERVICES PLANNING
After completion of an ATR a review of all the pending jobs is done and areas where job was not completed or delayed due to non-availability or late availability of material is identified. This is scrutinized and becomes learning for material planning in the next turn-around. Material planning continues throughout the year as per spare parts management and its criticality. Procurement process of material starts according to cycle time for purchase of the material.
Process departments identify their requirement related to job plan, which include electrical accessories, safety equipments (PPE), scaffoldings, platforms, approaches, other temporary arrangements and utilities like nitrogen required for purging etc well in advance. These are sent to respective department for making suitable arrangement in time. Administrative requirements are tied up in time in terms of arrangement of facilities etc for extra people for jobs.
It is preferred that all material requirements is send to stores & all material is received about a month before the commencement of annual turn-around. All these activities are reviewed in at the senior leadership level in the Apex Quality Council on a monthly basis. Similarly all service providers are short-listed based on competitive bidding process and each and every job is discussed with them in advance before he moves into site. They are communicated about our SHE policies and practices, maintenance procedures, ethical guidelines and codes of conduct to ensure effective delivery.
SAFETY PREPAREDNESS AND SAFETY WORK PERMITS
The top most priority at Tata Chemicals is Safety of people, equipment and machines. Utmost care is taken for all the personnel working in plant area. Before coming to work at site, the service providers and vendors are communicated about the site safety processes and procedures and are strictly asked to adhere to these. All their equipment that comes is inspected and certified by competent engineers before use at site.
Not even a single job is done without a safety work permit. This is strictly adhered for all jobs even in the non-critical areas. Before starting any job safety talk is given to maintenance people as well as contractor during hand over of permits. Safety work permit system is very robust and leaves no room for errors and mistakes. These permits are prepared by area process engineers and counter signed by safety officers depending on the criticality of the job. Additional engineers are deployed as safety managers for the turn-around period to have additional monitoring of the jobs with respect to safety. Risk assessment is carried out for all jobs and the precautions from that are mentioned in the permit. Detailed drawings of the equipment and circuit are attached with the permit showing the isolation and purging details. These are again signed by field supervisor before starting / after job completion & he is authorized to stop the job if he sees any safety or hazard issue. An example of a safety work permit and various precautions taken is given below:
Safety work permit for vessel entry
• Any first time entry in a vessel is done using on line air mask with lifeline by process people
• O2, CO, CO2, ammonia and explosive gases are checked, as relevant, by process as well as safety personnel & mentioned in safety work permits.
• Apart from the hand held meters, samples are also analyzed by lab confirm the results of gases
• Equipments are purged with nitrogen till “Zero” explosive for any hot job.
• Two people are appointed as a third party representative due to higher risk. Their responsibility is to check the circuit from schematic, isolation and permit. After they sign the permit, which is accompanied by a checklist and sketch for system isolation, only then the job can be started.
• The process for Buddy system is followed for vessel entry, which ensures that a stand by person is always present at the manhole of equipment with lifeline, and is in contact with person inside equipment through walkie-talkie.
• Caution boards along with safety ribbons are put out side the manhole during the period when entry remains suspended for an open vessel.
• For vessel entry under nitrogen atmosphere, one ambulance and an additional crane are kept all time for rescue operation.
• Arrangement for backup air supply for vessel entry of longer duration under nitrogen atmosphere (Like catalyst loading/unloading etc). e.g. We used one vessel (Blow down vessel – B602) for pressurized service air along with all instruments and safety valve as a back up for air supply failure. So if normal air supply fails then automatically supply from this vessel will start and people will come out safely from the vessel.
• We carry out mock drills to check our preparedness for rescue while people are working under nitrogen atmosphere.
• Emergency alarms on DCS & Local hooters are provided in plant area for low service air & utility nitrogen pressure. On blowing of these hooters, persons are taken out of reactors & vessel, where airline & nitrogen is being used.
PROCESS PLANNING – PREPARATION OF “SHUT-DOWN MANUAL”
The “Process Shut-down Manual” is a very vital document in planning & execution of all the jobs during shut down. This is a detailed document giving all the necessary information of the shut-down. The Deputy Manager of the plant along with his team is responsible for preparation of this manual about two months before the shut-down date. It contains things like:
• Schedule of shut-down and start up of each section of the plant (Fig 2)
• Final shut down job lists along with the tentative timings of handing over of respective jobs and receiving back from maintenance
• Planning of all major activities in form of Bar charts. (Fig 3)
• Activity charts for major jobs, including all steps with expected start & end timing (Fig 4, 5)
• Procedure for stopping all sections of plant, depressurization and purging details including schedule of purging various sections
FIG. 2: EXAMPLE OF SCHEDULE OF KEY SHUTDOWN AND STAR UP ACTIVITIES (SAMPLE ONLY)
FIG. 3: BAR CHART FOR SHUT-DOWN AND START-UP ACTIVITIES IN AMMONIA PLANT DURING ATR
FIG. 4: AMMONIA PLANT CRITICAL JOBS HANDOVER AND RETURN TIME PLAN
FIG. 5: BAR CHART FOR ATTENDING TUBE LEAKAGE FROM E 451 A/B AND E 432
• Procedures for isolation, handing for maintenance & safety precautions required
• Check lists for all job handover for maintenance
• Procedures for hydro testing/pneumatic testing of systems including circuits
• Procedures for special activities like catalyst loading, exchanger cleaning etc
• Checklists for emergency shut-down system and Instrument logic checking
• Manpower planning sheet for the entire duration of shut-down
• List of temporary lines, blinds required, hoses required, on line air masks, special lighting, power supply etc during shut-down
• General safety precautions and guidelines, etc.
The manual is then reviewed at various levels and inputs are taken from all levels from a field operator to the unit head for improvement. After final approval, the manual is placed at important locations like shift-in-charge office, DCS, and fielding operator cabin for information and training on shut-down activities. At field the shut-down jobs are provided with proper tags for easy reorganization during execution time.
Manpower planning is the next important phase of shut-down plan. The plants are divided into areas and sections depending upon the quantum of jobs and some of the senior persons are given responsibility of jobs execution in these sections. Manpower planning is done in detail & specific area wise for all the engineers and the field operators. All people area divided into day, night & normal shifts. Thorough training is given to all personnel for all activities well before shut-down. Detailed bar chart & schedule is made for all the critical activities.
During the entire duration of ATR special care is taken for every catalyst reactor. These reactors are kept under positive nitrogen pressure & bed temperatures are logged two hourly. Apart from the purging for maintenance this is the largest consumer of nitrogen in the complex. For this an accurate estimation for nitrogen requirement is to be done which is then communicated to the materials department for procurement. This requirement is over and above the nitrogen that we produce in the nitrogen plant.
EQUIPMENT HANDOVER
Equipment handover for maintenance is the most vital part of shut down because of the presence of highly flammable gases like hydrogen, methane, natural gas etc, toxic gases like carbon mono oxide, corrosive liquids like ammonia and carbamate and other hazardous fluids like naphtha, carbon dioxide, nitrogen, steam etc. For all such jobs, a team of experts does a detailed risk assessment & recommendations are included in detail shut down procedure. These risk assessments are attached with safety work permits during job. Adherence to the requirements of the safety work permit is ensured 100% and no lapses are tolerated.
The field operators and area engineer double check each and every job requirement before issuing any safety work permits. A good practice that we follow here is that all the permits are prepared by one engineer and the cross check is done by another engineer to identify any omissions.
Shut down procedure in the manual give detail of purging procedure with schematic diagrams, position of N2 hoses & purging points One such example of an ammonia synthesis section purging scheme is shown below in Fig. 6.
CHECK OF SAFETY SYTEMS AND TRIP INTERLOCKS
Safety of the plant is top most priority in Tata Chemicals Ltd. To ensure the safety of the plant each section plus all major equipment & running machinery is having separate start up & shut down logic control. All critical trips switch are provided with two out of three voting logic. All critical turbines, compressor & pumps are monitored through a state of art and dedicated machinery monitoring system (Bentley Nevada – TDM 2000). Each and every trip logic and interlock system is checked & logged in shut-down by both process & instrumentation personnel.
FIG. 6: SCHEMATIC SHOWING PURGING PROCEDURE FOR AMMONIA SYNTHESIS LOOP
All the trip, switches, vibration & displacement probes are removed, calibrated & recorded by instrument department. After installation process & instrument engineers crosscheck them through manual simulation. Each & every trip logic ladder is checked in SHUT-DOWNS. Stroke check of all control valves is done before start up. All critical PSV of equipments are calibrated during shut down.
For high pressure equipment in the steam system like boilers and exchangers statutory IBR testing is carried out at regular intervals at design pressure. Hydro test of all the critical heat exchanger is done at 150% test pressure and recorded in a checklist.
START UP PLANS
Start up of plant after a major turn-around is like starting up a new plant. It is an equally critical exercise as the planned shut down and we have to be prepared fro surprises. To avoid such situations each & every activity is very well planned. Each activity has a startup check list that helps field supervisor to DCS engineer in smooth start up. These check list are made through rigorous brainstorming & reviewed & upgraded annually. Every critical activity is kept in quick trend so that any deviation can be picked up very early.
Plant start-up activities starts with charging utilities e.g. cooling water, low, medium & high pressure steam headers through checklists & safe operating procedures. All the process equipments are purged with nitrogen to remove traces of air. It is essential to make good protective layer in all GV equipments so dynamic passivation of GV section done for at least 36 hours.
Nitrogen purging is done for all process vessels and circuits opened during shut-down in a predetermined sequence to avoid losses of nitrogen. Regular checking of oxygen is done by oxygen-meter as well as laboratory and the equipment is taken in line only after fully removing oxygen from the system. All such circuits that had been opened are first leak checked with nitrogen pressure of 5 kg/cm2g before taking gas in them. Leak check is done for all opened flanges by soap solution at this pressure and the same is repeated for all equipments once gas has been charged into them at different pressure levels. After leak check has been completed we go ahead with the actual start up activities like catalyst heating of pre reformer primary reformer, secondary reformer, MTS, LTS, by circulating nitrogen in closed circulation through a blower. Heating of Methanator and syntheses converter is done by process gas. All these activities are done by religiously following the start-up check lists.
PREPARATION OF SHUT DOWN REPORT
After successful completion of annual turn around and a steady start up it is time to take stock of the situation in terms of the benefits and learning from the ATR. All this is compiled in the form of a “Shut-down Report”. This is an important document which collects all the details, the good and the bad things from the shut-down and identifies the areas of improvement for the next such event. This comprehensive process report mainly consists of six parts.
• The first part covers the overall completion status of the shut-down jobs (whether complete or pending).
• The second part tells us about planned versus actual timings for major activities and jobs. This also tracks the timing of process activities like shut-down of different sections and start up of the plant etc. This helps us for planning the activities for next year.
• Third part contains the detailed observation of internal inspections and the jobs carried out inside critical equipment. This is recorded in standard formats covering date for handover, observations and major maintenance carried out.
• The fourth part contains the analysis and improvements achieved after the maintenance jobs. (Example attached – Fig. 7)
FIG. 7: SAMPLE OF TABULATING BENEFITS IN ATR 2006
• This fifth part is related to safety and environment for the period with the records of observations, near miss and incidents that occurred and the effluent generation report.
• The final part shares the learning out of our planning and execution for the shut-down period in terms of mistakes made, best practices followed etc so that it can be taken care of in the next opportunity.
Over the years this annual exercise of “ATR Execution” at Tata Chemicals Limited has really been systematized over the years and most of the activities have become standard. Apart from the error proofing and learning that has improved the processes there has been a huge quantity of energy saving and resource optimization that has taken place. Also the ammonia plant startup process has been optimized with various new interventions and the actual start up time has been reduced from 58 hours to 34.5 hours from start of reformer heating to ammonia production. This can be seen from the trend shown in Figure 8, which shows the tremendous saving in terms of GCals over the last few years. From a level of about 25000 GCals we have managed to come down to about 7000 Gcals in the last startup. Efforts are still on to further optimize this and achieve still better figures in the years to come.
FIG. 8: START-UP ENERGY OVER THE YEARS
CONCLUSIONS
It is a well known and accepted fact that shut-down or turn-around for chemical complexes are very vital with respect to future profitability. The execution of shut-downs requires lot of intuitive thinking and planning on the part of the process and maintenance engineers. At Tata Chemicals it is achieved through a continuous dialogue through out the year between both the process and maintenance functions and understanding each other’s requirements. Based on this philosophy we have successfully completed all nine shut-downs till date timely and safely with out a loss time incident. The plants have performed always better that the expectation after the execution of the shut-down.
