“This report was formulated & edited by Mr. M. Mehdizadeh [of Houston ,Tx (USA)] for Mr. Anand Joshi , Senior Partner ‘Manik Engineers’ who are the leading world class manufacturers (from Pune, India) of Valves, Controls & Monitoring Devices for the Industrial/Commercial Refrigeration & HVAC Industries. Mr Joshi is also the editorial chairman to India’s AAR Newsletter (Association of Ammonia Refrigeration) published monthly from Pune”
This is a case study on improving plant efficiency and safety of Ammonia Refrigeration System at a modern technology Ice Cream manufacturing unit. The plant is located at Cuttack near Bhubaneshwar, Odisha. The production capacity of the facility is designed for 10 MT of ice-cream per day for meeting the market requirements of Odisha and the neighboring states. We understood that walking around the plant can identify many small improvements that can enhance profitability. Also that an improperly operating unit required considerable field work. In walking between the control room and the main equipment, lot of discrepancies were noticed between the piping and its controls. Often these could signal heat gains from the environment which adds load to the existing refrigerating system.
The team from ‘Manik Engineers’ were called upon for troubleshooting of this plant and the directive from the owner was to upgrade in phases the existing refrigeration plant for higher efficiency and safety,fixing the heat gain problem while involving reasonable investment . Many a times plant upgrade /modernization leads to complete change of plant, whereby heavy investment and payback period of 3 to 4 years are estimated. Hence it was decided that plant improvement be based on saving energy while increasing capacity thru green design, aiming to achieve highest efficiency and safety management plan.
The objective further was to keep ROI period less than a year while achieving minimum 15% in energy savings. The refrigerant used in the plant is natural refrigerant, that is, pure(anhydrous) Ammonia , which earns a high environmental marks with ODP & GWP being Zero and in case of leaks, breaks down to its natural components of nitrogen & hydrogen in a relatively short time. This facilities’ refrigerating system operated thru natural (gravity) flooded feed.
NOTED PREVAILING PROBLEMS
Although today many people turn to IOT to quickly load up information, we decided to follow a systematic study to accordingly implement the above. The primary step was to prepare a HAZOP report and investigate operational plant problems on day to day basis. We proceeded by recording plant operation parameters and operating hours. Finally after careful study, the following problems were observed in the existing refrigerating system:
1. The chiller rooms and freezer rooms were not able to achieve desired temperature in spite of long running hours of compressors.
2. All unit compressors including standby units were required to remain in operation in order to meet the required refrigeration capacity.
3. The reciprocating compressors were running full load at all times
4. The compressor suction pressure and plant evaporating temperatures did not correlate. The suction pressure was much lower than the corresponding room temperature.
5. The compressor discharge pressure were high considering the ambient conditions.
6. Complete plant was being operated manually.
7. The air cooler coils for chiller rooms and freezer rooms would often frost.
8. Although the cold room and freezer rooms were designed at -25°C room temperature , however the best temperature achieved would be below -14°C.
9. The defrosting system was manual and was never able to defrost the coils completely.
10. Plenty of oil was getting accumulated in Freezer air cooler units’ coils.
11. With existing airborne contaminants, entrapped air or gasses, plant measurement techniques and/or measurement device accuracy were non-existent .
12. The level control system was bypassed and operators were manually throttling the valves on receiver supply line.
13. Freezer air cooler coils were starved for liquid supply , while operators feared possible liquid surge to compressor.
14. Operators were kept occupied by operating various valves applying extra efforts to check operation, temperature and liquid level.
15. Due to minor leakages through flange joints and some welded joints , strong ammonia odor was continuously felt in the machine room.
16. The chiller rooms and freezer rooms were located around the plant , and many times the operator would be trapped in temp controlled rooms, thus preventing the trapped person to freely communicate with plant operators.
Above conditions lead to high energy consumption and loss of production while overall plant was unable to perform at designated requirements. Also considering that the allocated budget to rectify the above was quite limited and in view of time constrain, we decided to concentrate on achieving desired roomtemperatures, increase plant efficiency and improve plant safety at shortest period of time . Another constraint faced was limited jobsite availability of highly skilled and certified man power to operate the plant. Hence it was required to provide an automatic operating system which can be easily handled by professional plant operators. The following functions were performed to update plant operations smoothly and trouble-free:
1. Installed ASME-approved dual Safety (relief) Valves on all pressure vessels with required pressure ratings.
2. Calibrated compressor safety cut outs , wherein these were also repaired and re-connected for safety.
3. Installed (on each compressor) easy to use Automatic Compressor control system with energy monitoring.
4. Installed fully automatic air purger on condenser and liquid receiver circuit.
5. Installed automatic hot gas defrosting system (replacing the existing manual defrost) on all air cooling units in chiller rooms and freezer rooms.
6. Installed temperature monitoring and control devices for all cold rooms and freezer rooms.
7. The automatic level control system was serviced and put into use.
8. Installed the reflex type level gauges and removed the glass tube one.
9. Installed an integrated automatic ammonia leak detection system.
10. All flanged type valves were replaced with 40 bar weld in-line valves. The valves were chosen with back seating facility.
11. The chiller room alarm system with built-in battery back-up was installed on machine room doors for trapped operator and generate alarm in plant room. This unit was incorporated within-built battery backup so that it can work independently in the event of power outage.
12. The overall above system improvement were anticipated to provide a Low Life Cycle Analysis (LLCA) and low carbon emissions where the refrigerating system gets greener and the energy savings add to the bottom line footprints.
Above performance was successfully implemented within 10 to 12 working days . This was done together with the valuable assistance of plant operators and one certified welder, without any downtime or disturbing status quo of plant operations. Once the required changes was in place and analysis performed within baseline and prevailing industry standards, a positive win-win results achieved were evaluated as follows:
1. The compressor discharge pressure reduced significantly to 160 PSI from 220 PSI .
2. The automatic operation of compressor units removed operator interference and resulted in automatic & smooth loading/unloading of each compressor. Additionally overall energy requirements on compressors were reduced significantly.
3. The safety valves and release system ensured increased safety at plant and no discharge of ammonia in plant in the event the safety valve pops up.
4. The automatic ammonia leak detection and alarm system increased plant safety meeting OSHA’s PSM safety requirements extending operator flexibility in working around the plant.
5. The automatic hot gas defrost system replaced manual defrost operation.
6. The defrosting period was reduced to 15 minutes instead of 45 minutes.
7. The increase in cold room / freezer room temperature during defrost reduced to 2°C from 10°C.
8. The cold room / freezer room design temperature of -25°C was successfully achieved.
9. The time required for freezer operation reduced by approx. 25% .
10. Numbers of operating compressors were reduced. The standby compressor remained as standby, and never required to operate , unless when called upon.
11. Reduced the compressor running hours by approx. 25%.
12. The automatic level control system made sure that ACU/Freezer coils are flooded thus preventing liquid slop-over to the compressor.
13. The automatic level control system avoided operator’s interference by installing throttling valves on receiver supply line.
14. Oil accumulation in ACU and freezer units were eliminated.
15. Frosting on ACU & freezer units were eliminated.
16. The installed online data logging and remote monitoring system helped customer to monitor the plant on mobile phone, (using the concept of IOT), while travelling enjoying their holidays.
17. The temperature control system made sure that required temperatures are maintained continuously. No under shooting/overshooting observed. All temperature were maintained within ±2°C
18. The weld-in- lines valves eliminated the leakages through the previous flanged joints.
19. The back seating facility in the valve assured operators that now they don’t have to pursue in tightening valve glands.
Thus, over all plant performance were improved by:
1. Reducing the plant operation time, hence reducing the plant deficiency period.
2. Achieving plant temperature requirements .
3. Operating at optimum suction and discharge pressures.
4. The ammonia odor from plant room vanished.
5. Increased plant safety and performance requirements.
6. The automation of compressor, defrost system, liquid level control and plant monitoring allowed operators address other maintenance issues.
7. By recording, monitoring and following relevant industry standards, solutions on safety and visual communication management throughout the facilities were provided .
8. All components, parts, units and devices involved on this troubleshooting works are engineered, designed & manufactured as “Made in India” products.
After observing a trouble-free plant operation for a period of one year, an estimated 30% energy saving was derived with an overall payback period recovered within 4-5 months. Additionally it also improved product (ice cream) quality and production capacity as compared to (prior to above improvement) previous year. Thus a well-done job was accomplished.