rehabilitation of a 1440 mtpd ammonia plant after 10 years

Rehabilitation of a 1440 MTPD Ammonia Plant After 10 Years Out of

Service Ammonia plant No. 5 utilizes M.W. Kellogg technology. It is located in the Cosoleacaque

Petrochemical Complex in the Mexican Southeast. It was constructed in 1975 and put into operation in 1977. The plant had been out of service since December 14, 2001 when, after 10 years, Pemex decided to start its rehabilitation, July 2011. In October 2012, the plant returned to production.

Francisco Morales Olán Cosoleacaque Petrochemical Complex, PEMEX – Petroquímica, México

Introduction

he ammonia plant No. 5 is a M.W. Kellogg design with an initial production capacity of 1360 MTPD (1500 STPD).

The plant was built and put into operation in 1977 and is located in the center of the Cosoleacaque Petrochemical Complex (CPC). It is State-owned by the company, Petroleos Mexicanos (PEMEX).

In 1999, the plant was revamped to increase its production capacity to 1440 MTPD (1588 STPD). Then, in December 2001 it was shut down due to the prevailing economics and high gas cost. Over the course of the next decade the econom-ics improved. A growing demand for fertilizer and low natural gas price was yielding a high profit-per-ton of ammonia produced. After be-ing out of service for approximately 10 years,

the Mexican State allocated funds to rehabilitate one of its ammonia plants in 2011. With a budget approved of 50 Million US$, work began in the summer of 2011 to rehabilitate the PEMEX ammonia plant No. 5 at the CPC, shown in Figure 1.

Figure 1. PEMEX ammonia plant No. 5 before the rehabilitation

T

1572013 AMMONIA TECHNICAL MANUAL

The information contained within this report of-fers detail to the stages of rehabilitation and ex-tent of work conducted to return the ammonia plant to production after being out of service for 10 years.

Initial rehabilitation work

Purchase Supplies, Spare Parts, and Chemicals

While most projects would consider the pur-chase of spare parts, chemicals and supplies to be of lower importance, this task was critical to the rehabilitation schedule. Being owned by the State, PEMEX and its purchasing system re-quired a period of time ranging between 6 to 9 months to acquire materials. Because of the po-tential impact on schedule, this process was ini-tiated immediately at the project start. The complete order was comprised of 109 req-uisitions, which covered the needs of all special-ties as follows: instrumentation, mechanical, maintenance of the plant, electrical, civil maintenance, complete pipeline circuits repairs, modification of the control room, repair of the primary reformer, training of operations, maintenance and technical staff, etc.

Eliminate Unsafe Conditions and Damaged or Corroded Plant Areas

Due to the continuous supply of moisture from a neighboring cooling water plant, as well as gen-eral environmental conditions, the plant sus-tained extensive corrosion, which required re-pair and replacement of damaged and corroded areas. There was also found to be extensive damage to the physical integrity of electrical circuits, the battery of process lines, and equip-ment. Figure 2 indicates the extent of corrosion in the Catacarb CO2 removal area of the plant.

Figure 2. Example of the extent of corrosion within Catacarb CO2 removal system The first goals in this stage of the project were as follows: Removal of insulation from all vessels and

pipelines, Removal of heavily corroded metal in dan-

ger of falling from platforms, Removal of all circuit piping in the condi-

tion of falling, and Removal of all dynamic mechanical equip-

ment (pumps) and interconnection lines. The estimated time to eliminate unsafe work conditions and remove and replace damaged or corroded plant areas was 90 days. Within the allotted time, approximately 80% of the risks associated with the existing plant were eliminat-ed.

Evaluate, Repair, and Rehabilitate

Furnaces and Boiler

Within the scope of the project were the evalua-tion, repair, and rehabilitation of furnaces and the auxiliary steam generation boiler. The fur-naces evaluated were the primary reformer, syn-thesis gas heater, natural draft heater, and in-duced draft heater fan. Each furnace and boiler was thoroughly inspected and rehabilitated in completion.

158 2013AMMONIA TECHNICAL MANUAL

The changes made to the primary reformer were extensive. The reformer is composed of 260 top fire burners with an additional 13 burners locat-ed at the furnace tunnels. The furnace required 90% of its metal plates to be changed in its walls. As well, a change to the reformer bed-spread refractory at the radiation transition zone and the auxiliary boiler duct was made. The single top-fire burners received maintenance, and all the support springs to the harps of cata-lytic pipes were changed. In addition the burner fuel gas supply lines were rerouted. In comparison, the primary reformer catalyst was found to be in perfect condition. Samples of catalyst were taken at random and checked to ensure they met acceptable physicochemical characteristics. The changes made to rehabilitate the synthesis gas heater were significantly less than compared to those of the primary reformer. The heater re-quired each of the five burners to be shifted, and the firebox enclosure required maintenance. The fuel gas circuit was also entirely changed. The feed gas preheater is a natural draft heater. The rehabilitation included changes to the 4 floor burners, repair of the firebox, and change to the enclosure mechanism. The gas supply line to the 4 heating coils was verified to ensure there was a continuous supply of gas and that there were no obstructions in the line due to the accumulation of oxides. As well, new instru-mentation was installed to allow for monitoring and control. The flue gas firebox of the induced draft heater was rebuilt in its entirety. The mechanical equipment of the induced draft heater was also changed completely. Figure 3 offers a compari-son, after rehabilitation.

Figure 3. Before and after photos of the in-duced draft heater fan The auxiliary boiler steam generator was revised and repaired in its entirety. The changes made were to the radiation box, metal plates, and beams of the frame. The four burners were changed, as well as the combustible gas and in-strumentation circuit. New ceramic fiber mod-ules were installed and the coils that recover heat from hot flue gases were inspected, evalu-ated, and pneumatically tested to ensure me-chanical integrity. The coils were found in good condition.

Turbine Pumps, Turbine Compressors, and Motor Pumps

There were 42 pieces of dynamic equipment which were evaluated in the ammonia plant re-habilitation: 3 turbo compressors

1 hydraulic turbine

22 pumps

16 turbo pumps The three turbo compressors were reviewed and rehabilitated in their entirety. Figure 4 offers a comparison between the 105-J ammonia refrig-eration compressor before and after rehabilita-tion.


Figure 4. Before and after photos of the 105-J compressor The remaining dynamic equipment was re-placed. A new hydraulic turbine was installed, and all motor pumps as well as turbine pumps were purchased new. The rehabilitation of each piece of equipment required a total repair of their bases, packaging lines, and suction and discharge pumps. As well, all electric motors were purchased new and all wiring to the motors was replaced. The new electric motors were high efficiency Nema Premium Motors, which allow contribu-tion to the conservation and protection of the environment. The high efficiency motors save power and generate less heat while operating.

Instrumentation and the Distributed Control System (DCS)

Ninety percent of the previous plant’s instru-mentation was changed, which included mod-ernization of the Foxboro Distributed Control System (DCS). Some replacements include the following: control valves for temperature, pres-sure, and level control, and conical threaded

thermowells. Another area which experienced a complete restoration was the vibration meas-urement system for the turbo compressors. Fig-ure 5 allows comparison between the old and new control room following the complete reha-bilitation.

Figure 5. Before and after photos of the control room Damaged areas of instrumentation circuits were changed and, at times, an entire circuit required replacement. The following instrumentation and controls were rehabilitated: Thermocouples and temperature elements

for compressors. Tachometer to control speed of the compres-

sor turbines, the induced draft heater fan, and the boiler feedwater pumps.

Digital speed control systems for rotating equipment.

Instrumented field boards. System-wide alarms and smoke detection

systems for ammonia and combustible gas. The electronic speed control and antisurge

system were upgraded to a modern PLC platform. The new system anticipates and prevents surge, on each stage of compres-sion, in real time.

Rehabilitation of the DCS included all updates and configuration changes, and complete func-


tional testing that included the corresponding field instrumentation. In addition, the uninter-ruptible power supply (UPS) was tested and up-graded. Components important for utilities, such as the instrument air pipelines and instrument air dry-ing equipment, were changed entirely.

High Voltage Electrical Circuits and Associated Equipment

Included within the evaluation, repair and reha-bilitation process, were the high voltage electri-cal circuits and associated equipment. Such equipment as the Motor Control Center (MCC), power transformer substations, electric motors, and lighting were each considered within this stage of the rehabilitation. As well, instrumen-tation in the form of electric, motorized valves and alarm monitoring was another consideration within this section of the project. An intelligent MCC was acquired in order to communicate with the DCS (Figure 6). The in-telligent MCC uses an automatic intelligent power switch that allows the operator to gener-ate a history, visualize and analyze the parame-ters such as power, voltage, amperage, etc., and identify possible causes for a shutdown. Anoth-er advantage of this MCC is that operation and monitoring of all electric motor parameters can be done from the DCS.

Figure 6. Before and after photos of the MCC Power transformer substations which use dielec-tric vegetable oil, FR3 were acquired. Use of this oil virtually eliminates the potential for fire and the enormous costs associated with this type of event. Use of FR3 also allows for improved transformer performance and increased loading capacity. The combined effects of these im-provements gave an estimated cost recovery of the investment within the first two years of op-eration. The power boards were rehabilitated to type 8BD of 13.8 kV. Another change included the total replacement of the lights with LED technology. Aside from electrical equipment, the electrical wiring also required extensive replacement. Approximately 110.5 km (68.2 miles) of wiring was replaced, of which approximately 6% was of medium voltage (between 4150 and 13800 volts) and the remaining 94% was low voltage electrical (600 volts).

Process Catalysts and Adsorption Media

Part of the plant’s rehabilitation included analy-sis of catalysts and adsorption media in order to evaluate their current physical states, after 10 years of inactivity. The ammonia plant has a to-tal of 12 process vessels containing several


types of catalyst and adsorption media as fol-lows: 1. Two activated carbon towers for desulfuri-

zation 2. Two sulfur guard vessels 3. Primary reformer 4. Secondary reformer 5. Two charcoal filters 6. High temperature shift converter (HTS) 7. Low temperature shift converter (LTS) 8. Methanator 9. Synthesis reactor

The following is a summary of the catalyst work completed: The activated carbon was changed in one of

the two desulfurization vessels.

The physical characteristics of zinc oxide (ZnO) and cobalt molybdenum (Co-Mo) catalyst within the guard chambers were evaluated, and they were in good condition.

The catalyst for both reformers was sampled for review and evaluation and was found to be in perfect condition.

The catalyst in the LTS and HTS was pur-chased and changed.

Both the methanator and synthesis reactor catalysts were found to be in perfect condi-tion and were not replaced.

Mechanical integrity and Maintenance

Static Equipment and Pipelines Circuits

A company was contracted to complete a study of the mechanical integrity (MI) for all process circuits and static equipment to ensure the relia-bility of equipment and pipelines. The study covered the design, manufacture, installation, construction, operation, maintenance and de-commissioning stages. The objective was to en-sure that each stage complied with the required

operating conditions such that workers, facilities and environment were protected.

Catacarb CO2 Removal System

The MI of the Catacarb CO2 removal system was reviewed in its entirety. To complete the review, all vessels were opened and inspected. The inside of the absorption tower was found to be in perfect condition and only minor work to the interior was conducted. The outside of the tower required additional maintenance. All screws and seals to the manhole were ex-changed, all process connection areas were re-paired in their entirety, as well as the mechani-cal integrity of its accessories was checked for maintenance, or change required. The CO2 desorption tower was reviewed follow-ing review of the CO2 absorber. Its interior was found to be in good condition also, and only mi-nor revisions were performed. The exterior of the tower had maintenance to install vacuum breakers in the dome of the tower. As well, similar to the absorption tower, the outside of the tower required additional maintenance to re-place all screws and seals to the manhole. Pro-cess connection areas were repaired in their en-tirety, as well as the mechanical integrity of the tower accessories was checked for maintenance and changed where required. Included in the desorption tower review were process connec-tion areas, which were changed. During the Catacarb CO2 removal system recon-struction, the following additions were made (see Figure 7): Five turbo pumps were purchased new, The hydraulic turbine received improved in-

ternals to allow for increased flow, and Eleven small motor pumps were purchased.


Figure 7. Five turbo pumps within the Cata-carb CO2 removal system were purchased and installed

Auxiliary Services

Another area requiring MI and maintenance were the auxiliary services, which comprised the following work: Inner packing of the cooling tower was

changed 8 cooling tower motors and their respective

fans were rehabilitated System-wide power supply was changed en-

tirely Cooling water pumps suction well isolation

gates were repaired 4 cooling water pumps had general mainte-

nance performed Removal of sludge and ferrous waste from

cooling water circuit Detection and repair of underground leakage Valve maintenance Rehabilitation of boiler feed water pumps Repair of boiler feed water system in its en-

tirety Rebuilt package steam generation boiler as

well as the corresponding steam pipes

Induced draft motor was restored Repair of the automatic ignition system in

its entirety Fuel gas supply circuit was built in its en-

tirety

Raw Materials Reception and Final Product Lines Rack

As part of the rehabilitation project, the MI and maintenance required for the product loading and unloading system was evaluated. In this section of the project, pipe wall thicknesses were a primary concern. Following measure-ment, pipe not meeting minimum thickness specifications was replaced or repaired. The product line rack has twelve different ser-vice lines. After conducting the MI analysis, it was determined that the heads for ammonia product lines to storage tanks, as well as for re-ceipt of ammonia for plant start-up, should be replaced. The line rack locks were changed en-tirely as well.

Resource Procurement and Integration

Third Party Contracts to Complete Equipment Procurement and Systems Integration

A necessary part of the ammonia plant’s reha-bilitation relied on obtaining third party contrac-tors to complete the necessary work. Each con-tract had established completion times which, in many cases, were limited by the completion of earlier projects. The most important projects to third party contractors were: Technical inspection and study of mechani-

cal integrity of equipment, vessels, and lines,

Rehabilitation of approximately 25% of the motor starters,

Rehabilitation of control room,

Repair of hydraulic cement in driveways, fittings and sidewalks slabs,

Rehabilitation and anticorrosion protection to pipelines, equipment, metal structures, stairs and railings,


Rehabilitation of hot and cold insulation on tanks and piping,

Rehabilitation of 13.8 kV electrical wiring,

Total rehabilitation of the cooling tower,

Rehabilitation of pipelines and supports (springs, cats and tensioners),

Total rehabilitation of the primary reformer, including areas of the penthouse, radiation, convection, induced draft heater and firebox, and

Total rehabilitation of the different various control valves.

As is evident by the above list, contractor man-agement and project completion time was a primary factor which enabled the success of this project.

Contract Maintenance Personnel, Skilled Labor, and Technical Staff

Contract maintenance personnel, skilled labor, and technical staff each played a critical role in project completion. During the rehabilitation of the plant, the number of onsite contracted per-sonnel reached approximately 1500 workers, each from various specialties, who worked with the 52 contract companies. A labor force skilled in mechanics, industrial electronics, and instru-mentation was recruited from all centers of Pe-troleos Mexicanos and reached an approximate total of 350 workers. 10% of the total workers were specialized and experienced technical staff. Figure 8 gives a depiction of contracted personnel during the final stages of the plant’s rehabilitation.

Figure 8. Contracted personnel aided the com-pletion of the ammonia plant rehabilitation

Hiring and Training Plant Personnel

Arguably, the most important resource to obtain is the right people. Manual operators (39) and chemical engineers (four) were trained to form the workforce of the plant and supervise the process control 24 hours of the day. Also a plant manager and supervisors were hired and trained in their respective departments. Manual operating personnel were drafted, call-ing for people with operational training in the process of ammonia, with priority given to those being supervisors with proven experience. The remaining personnel were recruited while con-sidering average experience in different areas and total knowledge of the process. The re-maining 50% of staff was recruited as new en-trants. Engineers in electronics and instrumentation, mechanics, construction, and electrical were re-cruited from within the technical staff of Petro-leos Mexicanos. The technical staff was trained for 6 months in the operation of the ammonia plant process, as well as the use and operation of the DCS. Chemical engineers and operators were trained in each area where they were to work. This


training was given by internal staff with over 25 years of experience in plant operation. The ser-vice of an external company was also contracted to apply an accelerated training methodology to improve operating performance. Training oc-curred over a period of 10 months, which in-cluded the time to learn how to operate the DCS. The plant manager was recruited and commis-sioned to oversee the development of the project from its inception, rehabilitation, receipt of new equipment, testing, and startup of the plant.

Commissioning, Testing and Production

Cleaning and Commissioning Reconstructed Process Circuits

Hydrostatic testing, pneumatic testing, and thickness measurements were conducted on re-constructed process circuit piping as part of the commissioning process. Fuel gas, process pip-ing, as well as high and medium pressure steam generation circuit piping were hydrostatically tested to ensure operational reliability. Car-bonate solution pipe circuits were evaluated in their thickness and washed (these pipes are stainless steel). Areas of pipe which did not meet thickness specifications were changed. As well, prior to operation, piping circuits were pneumatically tested in order to ensure there were no system leaks. Due to the high pressure operating conditions within the ammonia refrigeration circuit and to avoid potential release of ammonia to the at-mosphere, the system was pneumatically tested during the commissioning phase. These tests al-so ensured proper screw fastener and metal flange gasket tightness were achieved during the rehabilitation. Figure 9 depicts the ammonia re-frigeration circuit, following project completion.

Figure 9. Rehabilitated ammonia refrigeration circuit. Another aspect to the commissioning and testing stage involved checking all rehabilitated pipe welds by x-ray. In the case of the high pressure steam circuit, the stress relief in each weld was tested.

Testing and Startup

The testing and startup phase of the project was one of the final stages of the plant’s rehabilita-tion and timing played a critical role. The avail-ability of certain process circuits earlier in the project was necessary to complete the testing phase, prior to startup. For instance, the nitro-gen circuit was made available toward the be-ginning of the project to ensure proper inerting of equipment and lines. Similarly, the instru-ment air system was the next circuit of im-portance, in order to test and operate the control valves. From the initial startup and commis-sioning to production took 21 days. The first system to become operational during startup was the boiler auxiliary services pack-age, which generates 60 MTPH (66 STPH) of 41 kg/cm² (≈580 psig) steam. This steam was used to sweep the three steam pipe circuits op-erating at pressures of 105 kg/cm² (≈1500 psig), 41 kg/cm² (≈580 psig) and 3.5 kg/cm² (≈50 psig). Once the steam system was operational, cooling water pumps began operation to flow cooling water to pipe circuits and associated heat ex-


changers. Within this stage, the air-tightness in the water-cooled heat exchangers was tested. Availability of the package boiler and 41 kg/cm² (≈580 psig) steam allowed testing of the turbine pumps operating on this steam. The tests in-cluded setting and testing their high speed trip (OST). Availability of this steam also allowed operation of the induced draft fan for the auxil-iary boiler making it available to the process. The natural gas line was put into operation at this time in order to begin pre-production activi-ties. Work to pressurize equipment while moni-toring for leaks within accessories, pipes, gas-kets, metal flanges, man holes, etc. was begun. The reduction of the new high and low tempera-ture shift converter catalysts took place during the startup of the plant. The Catacarb CO2 removal system was the next system to become operational. Preparing the carbonate solution, maintaining its chemical control, as well as establishing recirculation through operation of the turbo pumps were im-portant tasks to begin operation of the CO2 re-moval system. Checks for leaks at metal flang-es and all accessories within the process circuit were made during this time. Following startup of the Catacarb CO2 removal system, the ammonia refrigeration circuit be-came operational through introduction of am-monia to the process. As was stated earlier, op-eration of the ammonia refrigeration system required extreme care and it is for this reason that it was pneumatically tested prior to opera-tion to ensure tightness and zero leaks before aligning the ammonia system.

Production and Stabilization of the Process

The plant began to produce on October 13, 2012. During the first week, a production rate of 500 MTPD (550 STPD) was maintained. During the second production week, the rate was increased to 1000 MTPD (1100 STPD).

Subsequently, an average production rate of 1250 MTPD (1380 STPD) was achieved and held stable for a period of one month. After a month, plant operation was stopped for a week to allow for repair and correction of defi-ciencies identified during operation. The outage allowed the following work to be performed: Review of turbo machinery components (in-

ternal, bearings, seals, etc.),

Correct functionality of some control valves, and

Stop flange leaks, packing leaks, etc. After the repairs and corrections were made, the plant was put back into operation and reached 1380 TPD (1520 STPD) continuous production. The production was maintained, without addi-tional hydrogen provided by the Hydrogen Re-covery Unit (HRU). The HRU receives the high pressure purge gas from the ammonia plant, separates the hydrogen from the purge gas, and returns it to the ammo-nia process at a minimum purity of 90.1%. With the HRU back in service, the improved H:N ratio has increased production approxi-mately 40 MTPD.

Conclusion

The high profit per ton of ammonia produced al-lowed recovery of the project investment in ap-proximately 100 days of continuous operation. Approximately 76,000 work permits were is-sued between the project inception and the time the process reached stability. The estimated man hours working time was ap-proximately 5 million hours. The stringent safety measures that were imposed to avoid accidents and serious incidents resulted in no lost time work accidents.


rehabilitation of a 1440 mtpd ammonia plant after 10 years

Documents