Process Set-up Revisit and Realignment: Reap the Benefits
P.C. Srinivasan
GM Technical
Chambal Fertilizers and Chemicals Limited

Rohit Shukla
DM-Technical Services
Chambal Fertilizers and Chemicals Limited

The technology provided by the renowned process licensors to produce ammonia and urea has undergone sea changes ever since their commercial production began in the bygone days. The state-of-the-art technology provided by the process designers has limited the scope available to reduce specific consumptions of ammonia and urea. Still fertilizer units present cross the globe leave no stone unturned to attain the lowest possible energy consumption level.

Fertilizer industries are in the midst of a transformation with regulation tightening by energy regulators like BEE, FAI, etc. Companies around the world have clamped down on costs and are exploring new ways to improve efficiency. Chambal Fertilisers and Chemicals Limited (CFCL) also strive to ensure that its energy consumption remains low. The present article gives some insights into one such successful in-house effort made by the company.

CFCL envisioned and implemented dual drive provision in the urea cooling tower (UCT) pump in its Gadepan-II urea unit by installing a new high tension (HT) motor. The UCT pump was formerly driven by steam turbine. However, the new motor is coupled with the same pump shaft but at the other end of the pump. Now, there is an option to drive the pump either through turbine or through motor, as the need arises. The pump is mostly driven by motor and the turbine is taken in line only during power shortage/outage.

Project identification, pre-engineering, bids floatation, vendor selection, detailed engineering were some of the pre-works involved. Challenges encountered before and after the modification with lucrative ROI offer interesting take away from the project.

Chambal Fertilisers and Chemicals Limited(CFCL) is one of the largest private sector fertilizer producers in India. CFCL has three hi-tech nitrogenous fertilizer (urea) plants located at Gadepan in the Kota district of Rajasthan. These plants deploy state-of-the-art technology from Denmark, Italy, United States, and Japan.

The first plant was commissioned in 1993, the second plant in 1999, and the commissioning of the third one was completed in 2019. With the commercialization of the third plant on 1st Jan 2019, annual urea production has touched 3.4 MT, making Gadepan India's largest single location producer of fertilizer. The additional capacity is of great significance to India as it results in the urea import reduction.

Project Pre-works
Provision of an additional electric drive along with a new pump requires clarification and pre-engineering in order to analyze the existing drive train, power requirement, foundation, and process control system to check feasibility and to calculate the return on investment (ROI).

Company's Gadepan–II unit is principally designed to run major drives on steam turbines. The power requirement is fulfilled by two Gas Turbine Generators (GTG). One GT always remains in operation with the other in tandem. The two GT-s are of 21MW capacity each and use natural gas as fuel. In GTG-1, inlet air cooling is achieved through VAM machine and therefore during summers GTG-1 remains in line while GTG-2 runs predominantly in cool ambient conditions.

Out of the 21MW GT output, Gadepan-II unit consumes merely 4-5 MW while the remaining power is consumed by Gadepan-I unit. Ammonia and urea plants run at 125 percent of design capacity, therefore GTG runs at its maximum capacity with only around 0.50 MW power margin. This margin (0.5MW) was not enough to commission any additional motor drive. This led to in-house brainstorming to increase the power margin in hand.

Deliberations then zeroed in onto reduce the overall complex energy. The committee mooted several ideas and one such idea was to install Variable Frequency Drives (VFD) in GV Lean solution motor & Boiler Feed Water (BFW) Motor drives in Ammonia-I plant and in Ammonia feed pump motors in Urea-I plant. In subsequent years, VFD was procured and installed in the above identified Ammonia-I & Urea-I plants, refer figure-2 for details of VFD installations in the Gadepan-I plant.

Through VFD's, the available power margin increased from 0.5 MW to 2.0 MW. With power margin (2.0 MW) at hand, the next challenge was to identify the drive which may be driven through motor without comprising operational flexibility, plant reliability, and safety aspects. In the entire complex, we could hardly identify any drive which may be driven through motor in entirety. Removing steam turbine was not a reliable solution as it would put plant reliability at stake during power outages.

Idea Evolution
It was then an idea evolved wherein it was decided to consider dual drive provision in Urea Cooling Tower pump in Gadepan-II plant. This UCT pump, erstwhile driven by steam turbine alone, now has a new motor (Rating: 1250 KW) coupled with the pump shaft at the other end of the pump as shown in the pictorial representation figure-3. With dual drive provision in place, flexibility to run the pump - either through turbine or through motor – has been enhanced. However, the pump is mostly driven by motor and only during power shortage / outage, the turbine is taken in line.

Fig-3: Pictorial representation of the modification

Challenges before execution
As every good move or intention is opposed by challenges, this modification was also not an exception. Some of the challenges CFCL faced during its execution are as under:

1. Space Limitation: Prime hurdle in the way of job execution was additional area required for motor foundation. The space available at the site was already limited and carving out additional area was a challenge with respect to free movement of cranes to address maintenance issues. The concern was brought to the notice of the motor vendor as well. Detailed engineering of the project identified and demarcated around 7.0 M2 area for the motor base frame and its foundation to suitably handle 8250 KG motor. Refer to Table-2 for motor static and dynamic loading.

2. Assigning safety interlock and alarm configuration: Defining new pump interlocks was not too demanding; however their seamless integration with the existing system was challenging. Nonetheless, the team's relentless efforts successfully countered every challenge in its way. Motor full load current (270 Amps) was defined to prevent the motor from overheating and subsequently burning up. Related alarms were also configured into the DCS for alerting the operator beforehand in case of any technical glitch.

3. Downtime requirement: For meeting Urea-II plant cooling water needs, three pumps are there and all three of them are steam turbine driven. Two turbines at a time used to remain in line, while the third one remained as emergency standby. For installation of motor along with pump downtime requirement was to be minimized. During the installation period, the turbine in tandem remained unavailable. And in case any of snag in the running turbines, plant capacity utilization had to be compromised. Given the criticality of the machine, downtime requirement for its commissioning was tried to minimize and in spite of that it took 17 days to complete the project. Please refer to annexure-I for the detailed scheduling of activities.

Challenges after execution
The challenges after the project execution were of miniscule nature, given the savings and benefits the modification brought along. However it is necessary to highlight the issues Chambal faced upon its completion.

1. Change in operation strategy: Prior to this modification , there were three steam turbine driven pumps. Amongst three, two pumps always remained in operation while the third one remained in tandem. With dual drive provision in the third pump, the operation strategy was later changed. And since then, the third pump with motor always remains in service alongside another pump to meet the Urea-II plant’s cooling water needs. This change in the operational strategy demanded training as well as change in mind-set for the operators.

2. Turbine declutching: As both pump and turbine are clutched with the same pump shaft therefore the turbine always remains declutched with the pump and whenever it is required to take turbine in service, it is clutched with the pump whereas motor is declutched. This is one-of-kind activity which is required only in case of any maintenance on the motor.

Savings and benefits
1. Tangible Benefits: The modification brought in energy savings of around 0.026 Gcal/MT Urea with payback period of nearly six months. This is almost equivalent to savings of ₹ 1.56 Lacs per day. Table-3 illustrates in detail the benefits accrued after the project implementation.

Table-3: Savings and ROI

2. Intangible benefits: In general, motors offer higher overall efficiency, optimized start and stop conditions, and more flexibility for operation.
a. Higher efficiency: Chambal could achieve higher efficiencies with commissioning of dual provision for the pump. It is a known fact that steam turbines are less efficient, compared to electric motor drive systems due to intrinsic heat losses from steam turbines.
b. Lesser maintenance: As earlier said, efforts are made to keep motor in operation and in general it is understood that motors, as compared to steam turbines, require lesser maintenance due to their simple & robust design and lesser ancillaries.
c. Reduced OPEX & enhanced reliability:Original steam turbine used to have more planned shutdowns due to its significant number of moving parts. The maintenance cost has been reduced gradually over the period.
d. Eliminating steam constraints: Using electric motor to drive the cooling water pump eliminated the steam dependency and the need for finding a high quality source. This improved availability and reduced both maintenance and resource costs.
e. Lower Emissions: As global emission standards became tougher, electrification contributed to a decarbonized energy future. A smaller footprint and less necessary auxiliaries made it possible to preserve the plant layout in more constrained environments and allow smooth plant integration.

Confederation of Indian Industries (CII) recognized the effort and declared CFCL as the Winner in the "2nd CII National Energy Efficiency Circle Competition" organized by CII in New Delhi. Contenders for this award were renowned technology providers, manufacturing giants, and institutions who showcased their success stories.

In order to successfully integrate the drive system into the process control, - careful coordination, planning, and combined efforts are the primary requirements. Chambal studied the economic advantages of electric drive systems meticulously, which resulted into significant operational flexibility, maintenance, and savings. Experiences so gained can also be directly used for similar retrofit applications.

Howsoever robust or well established a system is, there is always a scope for further improvement provided frequent system revisit & realignment happens to present day conditions meeting reliability, operational flexibility, and safe margins.