Heat Pipe Air Pre-Heaters in Oil Refineries An Alternate Approach
Background: Combustion air preheating by recovering heat from flue gases is a cost-effective method of increasing the overall thermal efficiency of the refining and petrochemical processes. Consequently, the use of Air PreHeaters (APH) in oil refineries has become well established and widespread in the last 4 decades or so.
Refinery operators have, however, over the years experienced well known problems with conventional APH types, these include:
- Reliability and maintenance.
- Premature failure & replacement.
- Inability to use in cold weather when internal acid condensation occurs.
- Excessive air leakage.
This article describes how Heat Pipe Air PreHeaters (HP-APH) address the limitations of conventional APH types and offer a proven and effective, alternative solution.
Conventional APH Technology
Many types of APH are utilised within refineries the most common types being plate & frame, DEKA and rotary wheel. Operators have reported a range of problems with APH equipment primarily caused by flue gas acid condensation which leads to premature equipment failure and air leakage. The problem is well understood by operators and equipment vendors who have developed a range of solutions to avoid acid condensation by maintaining minimum metal temperatures above the acid dewpoint of the flue gas. These solutions all require careful operation to avoid the occurrence of “condensation events” in the APH.
The effect of uncontrolled acid-condensation in a conventional APH is profound and usually results in corrosion breakthrough giving rise to leakage and cross contamination requiring service limitation and eventual bypassing.
Most conventional APH equipment is notoriously difficult to repair and often follows a path of reducing performance and eventual shut down.
The available acid condensation avoidance solutions are however limited in effectiveness and have a number of drawbacks including reduction of the APH performance resulting in lower energy recovery.
Acid Condensation Avoidance Solutions
Common acid condensation avoidance solutions include:
- Cold Air Bypass (CABP) – This involves by-passing part of the cold air stream around the APH to reduce the air volume being heated. This has the effect of elevating the lower air mass to an exit Temp higher than that required and by doing so increasing the minimum metal Temp in the heat exchanger. The bypass damper is controlled to keep the average of the flue gas exit Temp and ambient air Temp above the known acid dew point by a safety margin of 20F – 30F.
- Hot Air Recirculation (HAR) – This is often used in conjunction with the CABP and entails recirculating a proportion of the hot air exiting the APH back to the cold air inlet. This has the effect of elevating the temperatures in the APH in an attempt to avoid acid condensation.
The above solutions are only moderately effective at acid condensation avoidance but do reduce the overall effectiveness of the APH through reduction of the Log Meant Temperature Difference (LMTD). Furthermore, even with the use of a CABP and/or HAR, most operators lose a number of operational days per year where cold conditions dictate that the APH needs to be fully bypassed to avoid acid condensation damage. The costs of lost days of recovery is often not calculated and comes as an unforeseen additional production cost.
Heat Pipe Air Pre-Heater Characteristics
The HP-APH utilises as its heat transfer mechanism an array of heat pipes arranged in the hot and cold stream flows.
Each individual heat pipe within the HPAPH effectively acts as an independent selfcontained heat exchanger in its own right, this characteristic is extremely advantageous in that it creates significant multiple redundancy in the unit and addresses a key vulnerability in conventional APH equipment.
The table on the following page outlines the known issues with conventional APH equipment and how they are addressed in the HP-APH:
| Conventional Air Pre-Heater | Heat Pipe Air Pre-Heater |
| Issue | Cause | Differentiator | Beneficial Effect |
| Acid condensation formation | Acid condensation formation Difficult to achieve even temperature distribution in large APH equipment. This invariably leads to “cold corners” where localised acid condensation can occur. | By the laws of thermodynamics Heat Pipes are inherently Iso-Thermal. This property eliminates the possibility of “cold corners” and hence unexpected acid condensation formation. | By the laws of thermodynamics Heat Pipes are inherently Iso-Thermal. This property eliminates the possibility of “cold corners” and hence unexpected acid condensation formation. |
| Low minimum metal temperatures | The minimum metal temperatures in the conventional APH are largely a function of the ambient air temperature and the flue gas exit temperature. Whilst this can be calculated in practice because of the uneven temperature distribution throughout the unit it is unlikely to be accurate. | The heat pipe working temperature is not a simple average of ambient temperature and flue gas exit temperature. Through design this can be elevated significantly above the average of ambient and flue gas exit temperatures. | An elevated and known minimum metal temperature is advantageous in avoiding flue gas acid condensation. It also enables increased heat recovery by permitting lower flue gas exit temperatures. Use of CABP can be reduced or even avoided. |
| Vulnerability | Conventional APH equipment relies on thin metal surfaces to effect good heat transfer. There is an inverse relationship between heat transfer surface thickness and heat transfer coefficient. This creates conflicting requirements in that increased metal thickness is required for corrosion allowance but this has the effect of reducing heat transfer effectiveness. | The heat transfer coefficient of the heat pipe is less affected by the tube wall thickness than in conventional heat transfer. | Generally thicker material thicknesses can be used in the heat pipes Thus providing increased corrosion allowance. |
| Material Selection | Conventional APH construction does not readily accommodate mixed materials. The option of utilising Stainless Steel in the areas where acid condensation is most likely is generally not available. To build a large APH wholly in stainless steel is cost prohibitive. | As each heat pipe is independent it is possible to utilise SS material in only the colder end of the APH and non alloy steel grades elsewhere. | The mixed material approach combines cost effectiveness and additional protection. |
| Resilience | A corrosion failure in a conventional APH will result in immediate leakage and eventual withdrawal from service. | Each heat pipe is independent and self-contained. In the event of a pipe wall failure there will be no leakage as the pipe will still remain sealed in the tube plate. | The impact of individual heat pipe failure is minimised. |
| Maintenance | Conventional APH equipment is notoriously difficult to repair once corrosion damage has occurred. At end of life a whole unit replacement will be required | Heat pipes are individually replaceable. | Heat pipes are individually replaceable. Whole unit replacement is avoided as individual heat pipes can be changed on site without the need to uninstall the unit. |
| Control | It is not practical to measure the true minimum metal temperature in a conventional APH due to uneven temperature distribution. The protection against acid dew point condensation therefore relies on calculations of ambient air temperature and flue gas exit temperature rather than on real time measurements. |
Within the HP-APH the precise locations of coldest spots are known through design. This enables real time temperature measurement of selected heat pipes in the coldest row of the APH. | The coldest pipe real time temperature can be used to control the CABP to ensure that flue gas exit is targeted to minimum acceptable temperature hence maximising heat recovery duty whilst avoiding acid condensation.. |
By way of simple comparison with conventional APH types it is the case that the HP-APH offers the benefit of REDUCED RISK of failure and REDUCED CONSEQUENCE of failure. Evidence of fully operational HPAPH equipment installed in the 1980’s and 90’s confirm the longevity of the HP-APH in even the most aggressive and demanding conditions.
Retro-Fit Flexibility
The HP-APH is available in a variety of configurations and can be custom designed to accommodate minimum ducting changes as a retro-fit replacement for a failed or end of life conventional APH equipment.
All units incorporate temperature sensing heat pipes in key locations and also feature up to 4 rows of stainless-steel heat pipes in the cold end of the units to accommodate any transient condensation during start-up and shut down conditions.
For further information or equiries, please contact:
Mark Boocock
Econotherm (UK) Ltd
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
This email address is being protected from spambots. You need JavaScript enabled to view it.
Web: www.econotherm.co.uk
Tel: +44 (0)1656 658640
More Than Just a Frame System
Global Gravity was established in Esbjerg in 2011, and specialises in transporting casing, tubing, and drill pipes for the oil industry. The company is the inventor of the patented TubeLock system, which is the world’s first “Tubular Transport Running System” (TTRS).
With TubeLock, Global Gravity are taking care of all handling and transportation of all types of casing, tubing and drill pipe tubing from storage, across the quay to the ship, and onto the drilling rig. TubeLock improve safety and efficiency significantly for the offshore operators.
Pipe handling can be quite a dangerous job if it is not carried out correctly and because of threats from the outside. Every day, the crew work in harsh conditions, exposed to wind, cold and noise in a very challenging working space. There is a great risk of injury to people and damage to equipment. It is not far from the walkway to the edge, and bulldog clamps and tools have been dropped on several occasions. With traditional wire slings heavy loads of pipes are rolled out, stacked and bundled with 10- to 12-metre-long steel wires, causing danger to the people working when unloading and dangerous stored energy released when the slings are removed from the bundled pipes.
TubeLock reduce these risks as the pipes are stored and transported in a safer manner and are stacked according to all safety criteria. With TubeLock there are less manual handling and most preparations can be done onshore.
Furthermore, surveys show that customers reduce time spent on the overall handling process by 50% compared to the traditional solutions. At the same time, TubeLock requires 50% less space and halves the amount of handling out on the drilling rig. Using the TTRS Systems you can run the tubulars directly out of the TTRS frames as they are all measured and numbered. You can run the pipes directly into the wellbore from the TubeLock system, therefore there are no requirements for the rig crew to unload the frames and lay the tubulars out on the pipe deck reducing the handling of tubulars on the Rig and supply boat by 50%.
It is a documented fact that our operators save 50% of the time normally used moving pipe from supply boat to cantilever deck on the drilling rig ready to be run in hole. The time saved offloading boats free the deck crew and cranes for more important tasks related to the drilling operation. And saves both fuel on cranes and supply vessels during the operation.
As pipes does not have to be laid out upon arrival on the rig, handling is reduced by at least 50% thereby reducing risk of dropped objects and injury to personnel.
TubeLock is certified as an offshore lifting appliance under DNV ST-0378 and Norsok R02 and is in compliance with ILO and LOLER recommendations.
TubeLock is manufactured from Aluminum to ensure it is easy to handle and no single part weight more than 15 kilos. The aluminum base product also ensure there is no galvanic corrosion between TubeLock and chrome alloy tubes
Sand-Screens is yet another product that we have successfully transported, saving the operators time and space by not having to use large transport baskets which take up cumbersome space on the supply vessel even when returned empty. The cost of chrome and super chrome tubulars are some of the highest costs when drilling and completing wells and there is a high risk of damaging these tubulars when bundling and slinging Chrome Tubulars. When these tubulars are transported in the TTRS frames they are protected and cannot be damaged.
A work group set up by UK Oil and Gas and Step Change to review lifting incidents, has highlighted the practice of bundling and slinging tubulars to be a high risk process and that we should work to eliminate that process within a timeframe agreed by all industry participants.
“We believe that TubeLock® TTRS will be the future for all involved with pipe transport, storage, inspection and drilling.”
Our Track record is as follows:
- UK Operations – 3-1/2” to 9-5/8” (Equinor – 13 wells)
- Qatar Operations – 3-1/2” to 13-3/8” (North Oil Company – 5 year contract - 4 No. rigs )
- Denmark Operations – 3-1/2” to 13-3/8” (TOTAL – 5 Year Contract)
- Australia Operations – 4-1/2” & 7” (Santos)
- Trinidad Operations – 5-1/2” Bakers Sand Screens (BHP)
- Norway Operations – 4-1/2”, 5-7/8” & 7” (Var Energi, AKER BP & Neptune)
- Holland Operations – 4-1/2” to 9-5/8” (Tulip Oil, Wintershall Noorzdee BV, NAM)
- Germany Operations – 2-7/8” to 9-5/8” ( Wintershall DEA – 5 Year Contract)
Global Gravity supply the world´s first Tubular Transport Running System (TTRS). TubeLock® provides optimization of all processes for pipe handling within all types of well interventions and drilling operations around the world. Giving our global customers great cost savings in combination with the safest and most effective TTRS for all types of pipes used by drilling rigs.
If you would like to know more about how Global Gravity can help your company and its operations, please contact them at:
Global Gravity ApS
Tel: +45 71 99 20 10
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Web: https://www.globalgravity.dk
We Create the Tools to Get the Job Done - Not Just Report the Problem
Together with local and global clients, RoQC aim to strengthen data quality assurance and increase data quality by applying strong domain knowledge and innovative software solutions within Subsurface & Drilling Data Management. The RoQC software suite (RoQC Tools) represents unmatched time-saving and efficiency gains in Data Management. RoQC Tools provide integration, extended and unique functionality and workflows to the Petrel*, Studio*, DELFI*, OSDU*, EDM* and Openworks* subsurface technology environments.
You can read more here.
On-Site Oil Analysis for Condition Monitoring of Complex Machinery and Hydraulic Systems
Offshore oil and gas production platforms require reliable condition monitoring programs of lubricants and fluids to provide continuous and safe operation of the critical offshore machinery under harsh environmental conditions. Due to their remote location, oil and gas platforms may not be easily reached by highly trained personnel to make equipment replacement in case of machinery failure. Any major breakdown can substantially hinder the work of a platform or might pose a safety hazard to the operating crew. Moreover, repairs in offshore oil and gas industry can be very expensive and time consuming. In opposite, application of on-site oil analysis program to monitor the condition of essential parameters of lubricating oil and fluids is easy, smart and cost-effective solution which can be adopted as a part of the successful equipment maintenance strategy, i.e. machinery and hydraulic systems required for energy production for offshore oil and gas platforms (e.g. diesel engines, gearboxes, turbines, pumps, compressors etc.).
Alternative Approaches to Oil Analysis for Optimization of Machinery Condition Monitoring
As a rule, the prevailing practice of oil analysis for monitoring the operating condition of the equipment presumes oil sampling every two to three months and using an onshore laboratory for analyzing specific oil parameters. However, taking into account offshore and remote location of oil and gas platforms, the laboratory results may not reach the operating personnel and technicians responsible for equipment maintenance for several weeks. Such delays in obtaining oil analysis results may lead to failures in identifying existing maintenance issues at the right time and cause unexpected downtime of the machinery.
An alternative approach to oil analysis is the adoption of on-site oil condition monitoring programs through the mechanism of regular or continuous assessment of the critical oil parameters of lubricants and fluids such as water-in-oil, alkalinity reserve, viscosity, acid number, the presence of insoluble and metal particles etc.
Martechnic offers two different oil condition assessment techniques that can be used for maintaining operational equipment of offshore oil and gas platforms:
- Regular interval-based determination of lubricants’ condition with the help of portable test devices;
- Intelligent monitoring with sensor technology for an unattended machinery space.
The main advantage of these analyses methods is the possibility to provide accurate information on the actual condition of the lubricating or hydraulic oil in use and to detect any occurring irregularities or abnormal processes prior to unexpected catastrophic failures.
Portable Testing Equipment: Trend Analysis of Oil Condition
Regular oil condition monitoring with portable testing equipment is an easy and quick on-site method which provides almost immediate and high accuracy test results. The operating personnel is able to routinely check crucial parameters of lubricants and hydraulic fluids. When individually establishing monitoring intervals for each oil parameter of interest, technicians collect data for tracking trends in the oil condition to make a prognosis and accordingly to plan efficiently on necessary maintenance time.
If an abnormal oil analysis test result is obtained, a repetitive measurement can be conducted by the crew to confirm the accuracy of the measured parameter before a further corrective action should be considered. This can help to reduce expenses and/or predict potential problems or equipment failures prior to their occurrence.
The test kit “LUBE OIL CHECK OS” of Martechnic combines portable test devices for five different on-site lube and hydraulic oil tests that are crucial for condition monitoring and maintenance of the key machinery of oil and gas platforms.
Water-in-oil and alkalinity reserve of lubricants can be measured with the test device “TWIN CHECK 4.0”. The test device measures automatically and precisely both parameters through the built-in pressure sensor which registers pressure build-up in accordance with the degree of water concentration/ BN value in the oil under examination. The “TWIN CHECK 4.0” is offered in modular design with possibility to replace every single constituent part and has a USB to serial cable connection and memory chip for data storage and trend analysis.
Alongside water-in-oil and BN monitoring, the “LUBE OIL CHECK OS” offers a quick “go/ no go” viscosity test to immediately identify any deviation from standard viscosity values. Spot test can help to regularly determine occurring changes in the oil condition and is primarily used for assessing the level of soot contamination of engine lube oil.
With respect to hydraulic systems of the oil platforms high operating temperatures or ingress of aerial oxygen can lead to oxidation and nitration of hydraulic fluids and occurrence of acid sludge. Early detection of increased acid value with the test “MT AN CHECK” can help to avoid further degradation and to protect machinery through scheduled maintenance.
Intelligent Sensor Technology: ConditionBased Maintenance of Complex Machinery and Hydraulic Systems
Remote location of oil and gas platforms and often scarce operating personnel resources for regular oil condition monitoring of complex machinery and hydraulic systems may be the factors to prioritize an installation of permanent oil condition monitoring devices, i.e., intelligent sensor technology.
In contrast to portable testing equipment, permanently installed in-line sensors provide continuous 24/7 oil condition assessment, when principal oil parameters are monitored in the real-time mode. Automated alerts with early warning system provide immediate notification of occurring changes of the oil parameters and enable maintenance crew to analyze the problem and to take necessary maintenance measures at the pre-alarm level during the uninterrupted operation process of machinery. In its turn, equipment maintenance intervals can be optimized and possibly prolonged.
Martechnic designed and developed an innovative MT MODULAR MONITORING SYSTEM for comprehensive and continuous oil condition assessment. The principal benefit of the system is its modular design, namely the possibility to customize a version suitable for a specific field of application in accordance with individual requirements and to install the sensors into specific machinery components (generators, gearboxes, mud pump bearings, hydraulic system etc.) depending on the oil parameters to monitor.
Appropriate lubrication is the prerequisite for flawless functioning of machinery components. Due to increased humidity of marine environment, lubrication system may be exposed to moisture condensation and occurrence of water.
Continuous measurement of water-in-oil content, for instance in gearboxes, can be made with the infrared AHHOI IR SENSOR. The sensor measures water concentration in molecular form in the range of up to 10000 ppm / 1.0 vol. % and enables determination of water in all three states: saturated, emulsified and free. The sensor is installed in the bypass and can be equipped with manifold for simultaneous monitoring of up to four different oil systems.
HUMIDITY SENSOR can be applied for generators and will enable determination of any unexpected rise in the level of relative humidity of oil in % (ranging from 0 % - no water detected to 100 % - complete saturation/ existence of free water) through continuous measurement of the degree of oil saturation with water.
PARTICLE SENSOR is useful for immediate detection of the increased degree of concentration of insoluble particles in oil. FE SENSOR helps to monitor oil system contamination with ferromagnetic particles.
Simultaneous application of several permanently installed condition monitoring sensors and their connection to the special display unit DATALOGGER for continuous data recording and assessment can offer a reliable and secure solution for conditionbased maintenance of complex machinery and hydraulic systems.
Conclusion
On-site oil analysis and adoption of oil condition monitoring programs can be considered essential for managing safe, continuous and efficient operation of critical machinery of offshore oil and gas platforms. Implementation of a preventive maintenance strategy with well-planned maintenance intervals may help to optimize the overall performance of the operating equipment and to contribute to providing of uninterrupted production of oil and gas platforms, therefore also effectively protecting the marine environment.
For more information on condition monitoring of lubricating and hydraulic oil, please contact Martechnic:
Martechnic GmbH
Phone: +49-40 853128-0
Fax: +49-40 853128-16
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Web: http://www.martechnic.com
It’s Important to Spot Every Drop
Ruben Østrem, Finance & Marketing Officer, from ProAnalysis AS helps OGI and our readers understand the importance of using the best tools for your oil in water testing and why
reliable measurements of oil in water is critical for produced water treatment, especially due to increasing water volumes in tale end production.