Refrigeration systems are widely installed in India more than 60 years now. We have developed knowhow and technology to manufacture refrigeration equipments in India. We also have design, engineering, installation and commissioning knowledge for refrigeration system.
India is widely using Ammonia – a natural refrigerant for more than 60 years. We have lots of refrigeration system – for example: installed refrigeration system for cold storages and food processing industry, which are more than 20-30 years old. They were designed and installed with technology available during those years.
Initially when a plant is new, we may not get clear picture about plant performance, energy consumption and safety. When the plant becomes old – say around 3 to 4 years, actual energy consumption becomes more evident. More thrust is given to production / maintenance of temperature, rather than plant performance and safety. This results into deterioration of plant performance, more energy consumption, increase in running hours of compressors and increasing cases of breakdown than initial stages along with increase in operating cost.
As a plant owner, we must ask the following questions to ourselves:
I already have an existing plant and I need to know the following:
Whether my plant is optimized?
I have already modified my plant to get better performance, but am I getting that?
Is my plant energy efficient?
Is may plant safe and easy to operate?
Whenever I visit the refrigeration plant room, I smell ammonia.
Is my maintenance cost increasing day by day?
Are breakdowns increasing?
Is always any one of the equipment under breakdown?
One must start asking the above questions and take suitable action accordingly.
Once we start asking these questions, then it consider this as a first step for improving plant performance and safety.
In order to know the answer for the above such questions we suggest taking planned logical steps.
First thing is to form internal team: The members of the team must be fully motivated, ready to devote time – and are enthusiastic to take up this task.
Second step is to conduct external technical Audit: Even though our team is operating the plant day in and out – and has sufficient in-house expertise, it is recommended to appoint external agency to audit the plant. The external auditor carries out an unbiased study of the plant and that will help in achieving better end results and objectives.
Third step is – study the external report and take suitable actions to achieve the goal.
Before we start any of the activities, we must study the following Table 1. This table indicates approximate percentage of installed kW of major equipments in total refrigeration system in a low (-25 Deg C) room temperature cold storage.
Table 1: % of total refrigeration plant installed kW
Keeping in view of the above let us see advantages of audit to improve the existing plant performance and increase safety of the plant.
1) Check existing basis of design and if required formulate proper revised basis of design of existing plant:
We must formulate existing plant basis of design if not available. During the years we might havemodified the plant or removed certain equipment or add more load to existing plant. It is always better to write down the present refrigeration load w.r.t respect to our installed plant refrigeration capacity.
2) Check existing plant operating parameters:
We must check and evaluate existing plant operating parameters such as evaporationtemperature / discharge pressure our plantas it directly affects the energy bill.
2.1) Effect of evaporation temperature on energy bill: If Cold room temp required is0 Deg C. The evaporation temperature to achieve this temperature should be -5 Deg C. If we observed that we are operating the plant say at -10 or -12 Deg C. This will directly results into higher electricity bill. We need to then find out and if required we have to rectify the existing system so that our plant operates at desired evaporation temperature. The following table-2 will indicate effect of evaporation temperature on electrify bill.
Table -2 Effect of evaporation temperature on energy bill
Install properly designed system to control desired suction pressure. The payback period for such properly engineered and designed system will be approx. two years for positive temp system and approx. less than one year in case of low temp system.
2.2) Effect of discharge pressure on energy bill: Check at what discharge pressure the plant is operating w.r.t designed discharge pressure. Following Table -3 indicate effect of higher discharge pressure on energy bill.
Table -3 Effect of higher discharge pressure on energy bill.
The high discharge pressure can be due to non-condensable gases in the system.
The properly designed and installed system to remove non condensable gases has payback period less than one year.
3) Check installed equipment selection w.r.t our operating parameters and from energy saving point of view.
Evaluate major installed equipment like compressor, condenser, air cooling unit for their operating parameters and performance. Study the findings and advice given by the external auditor and take action as recommended. We give below some of the example in this regard.
3.1) Check selection of compressor w.r.t. required operating evaporation temperature:
For example: If it is observed that single stage compressor is installed to operate at -30 Deg C evaporation temperatures. If we replace this single stage compressor to two stage, we will achieve considerable energy saving. This is shown in Table -4 below.
Table 4: Following table indicates the energy saving achieved by replacing single stage compressor by two stage compressor for -30 Deg C evaporation temperature operations.
Table: 4 Single stage v/s two stage compressors.
As per experience, the payback period for above replacement is less than six months.
3.2) Check performance of existing condenser and possibilities of any energy saving:
We give in Table: 5 comparisons of various types of condensers and energy saving possibilities in the same. Table: 5 comparisons of various condensers
4) Plant Automation:
Check whether automation is installed or not. Various automation levels can be incorporated based on plant type, skilled man power availability.
The recommended approach towards automation is as below:
To reduce Human dependence on plant maintenance.
Automatic Parameters recording to avoid human error and intervention while recording.
We should be able to monitor plant parameters any time and from anywhere.
Automation to be developed to helpoperatorto operate plant at desired parameters and avoids excess energy consumption due to operator error.
Operator frequently throttle valves installed at liquid Header (going to cold room) from plant room to avoid liquid stroke to compressor. Automation avoids this and operate can devote more time on more fruitful work than this.
Based on above it is recommended to evaluate the status of existing plant automation and follow the expert advice to develop automation to suit specific plant requirement.
5) Study plant safety point of view:
Study the safety interlock, ultrasonic test reports, pipe condition, support condition. Take action as recommended by the expert to make plant safe and easy to operate.
Next to this, we are giving some of the photographs of the plant before and after audit which made the plant safe to operate.
5.1) 35 year old receiver replaced by new – as old receiver as we observe that thickness of receiver was drastically bad – and it was unsafe to operate.
Along with housekeeping, please check and evaluate whether receiver spray shower is working or not, all personal protective equipments are in proper condition or not, ammonia leak detection system is installed or not, if installed it is in operation or not. If any discrepancy is observed, then it is recommended to follow the expert’s advice and comply with the same.
To conclude following are the points to remember:
It is very much possible to achieve desired energy efficiency throughout the life of the existing plant.
With proper guidance and SOP in place every year we can improve /maintain desired plant performance.
Prepare preventive maintenance schedule and strictly follow to minimise breakdown.
Analyse/ evaluate every year present operation properly to optimise the plant operation. This will help in increasing production, improve quality, improve performance and save energy.
While replacement of equipment
Optimise Capex along with Opex.
Any such modification for plant performance improvement does not cost high. Normally payback period is less than two years.
