The oil and gas industry needs efficient cooling, given the region’s ambient conditions. In light of this, Imran Ali highlights issues involved in process cooling and suggests solutions.

Introduction

The importance of the O&G industry cannot be understated, as it is the backbone of the world’s economy and the future of industrial development and growth in the region. Due to its complex and sensitive nature, it demands high standards of service and support. However, it is not uncommon to come across issues related with performance deration, efficiency limitation and loss of productivity. All these factors are, undoubtedly, very significant, given the magnitude of the projects.

Typical related sectors within the O&G industry where the aforementioned problems could occur are:

• Petrochemicals
• Refineries
• Process industries
• Power plants
• Off-shore rigs & platforms

Typical process cooling applications are:

• Dense air injection
• Condenser cooling
• Reactor cooling
• Supplemental water cooling
• Lube oil cooling
• Gas turbine cooling
• Air-cooled motor cooling
• Shutdowns – temporary power and cooling for labour camps, auxiliary power for critical areas, cooling down vessels, reactors, etc.

Air limitation problem due to ambient conditions

This is one of the most common situations, especially in the Gulf region. This is because of the five months of high-ambient conditions when all types of industrial process struggle to cope. However, these issues can be tackled on a proactive or even reactive basis, in case of emergencies, if one is armed with the basic concepts of thermodynamics.

Suggested solutions

It is possible to cool large volumes of air and deliver or introduce chilled air into the intake on the regenerator’s main blower, thereby simulating springtime conditions.

Closed loop system:

In a closed-loop system, air-cooled water chiller circulates 7°C water through an air-handler equipped with a high-static blower. Ambient air is normally cooled to 15°C. The cooled air is forced through temporary duct work which is directed at the intake to the air blower. The 15°C air is, then, mixed with ambient air in whatever quantities, to give the desired effect.

Here, it needs to be noted that the basic concept of cooling is to remove the heat to make the area cool. Thus, once dense air enters the area, it pushes hot air out. This is, in fact, the reason why extractor fans are installed close to the ceiling, as hot air (which is lighter in mass) travels upwards, while dense air (which is heavier in mass) does the opposite. Please see the process diagram, below.

Summarised study

In a typical plant room, motors, turbines or generators are normally rated at 40°C to 45°C, and will always be on the threshold of their optimal performance during peak summer season. In this scenario, deration will start affecting the performance as soon as the temperature rises, and goes beyond the rated temperatures. The other important factor is that within the plant room, the temperature is always on the higher side than the outdoor ambient conditions, mainly because of the thermal heat rejection and improper ventilation. Studies show that the range of increased temperature within the plant room is always 10°C to 20°C in surplus to the machine’s actual rated conditions from OEM. Therefore, it does not reflect the true picture that will help gauge the performance, while considering only the outer ambient conditions.

In a typical scenario where the outdoor ambient condition reaches beyond 45°C, it may result in an additional 10°C to 20°C overheated plant room, duration, which will be in the range of five per cent to 20%, while in most cases, an average 10% deration is observed. For example, if a plant room has a generating capacity of 10MW, it will only be producing 9MW, while consuming the same amount of operational costs (ie, fuel, maintenance, manpower and repairs) required to produce 10MW. The effect of not reaching the required performance will obviously result in higher cost ($/KW-Hr) and reduced profit ($/KW-Hr). However, the cost comparison to recover this performance loss is very minimal, as temporary cooling modules like chiller+AHU or DX/packaged units can be used to supply dense air injection to improve efficiency to bring it back to the optimum condition.

Tri-gen:

A good solution would be to install a small CCHP (tri-gen) on a permanent basis. This will recycle the exhaust air and process it into steam and, then, cool it through an absorption chiller. It will subsequently use the chilled water for air conditioning within the plant to create an effective ambient condition and/or use it for other process cooling requirements. It is, in fact, a win-win situation, as it does not use additional fuel, while at the same time, reduces emissions.

The writer is General Manager at Argonaut Rental Division – GCC Region. He can be contacted at imran.ali@argonaut.com