This document discusses several strategies to enhance energy efficiency in the thermal oil system of a gas processing plant. It identifies optimizing excess air in thermal oil heaters, improving specific energy consumption in amine treating units, utilizing waste heat, reducing energy losses in thermal oil distribution pipes, and optimizing pumping systems as key opportunities. Case studies demonstrating energy and cost savings from these strategies are provided. The document concludes that a multi-pronged approach is needed to maximize energy efficiency in thermal oil systems in gas processing plants.

1. Enhancing Energy Efficiency of
Thermal Oil System in Gas
Processing Plant
Cahyadi1,a), Taopik Hidayat1, Yusuf Ahda1, Tata Sutardi1)
1Research Center for Energy Conversion & Conservation
National Research and Innovation Agency
KST BJ Habibie, Serpong, Tangerang Selatan, Banten, Indonesia
Email: cahy004@brin.go.id

2. Background
• Based on energy conservation program as stated in the
Government regulation No. 70 year 2009, Gas processing plant
has to implement energy management system.
• Energy Management System as mentioned in Regulation of
Energy and Mineral Resources Ministry No. 14 year 2012 or ISO
50001.
• In EMS , we need to identify the Significant energy use (SEU).
SEU is the list of main equipment in the industry that contribute
to the top 80% of energy use.
• Thermal oil heater usually as one of the equipment in SEU.
• Energy efficiency in gas processing plant is very important for
modern gas processing plant, essentially due to the high cost of
fuel as well as limited gas resources. Efficient processes with
lower energy intensity also reduce greenhouse gas emissions
and also reduce the natural gas fuel for internal energy use.
Energy audits, metrics and benchmarking are valuable tools for
achieving maximum energy efficiency.
GPP Plant 1
GPP Plant 2

3. Thermal oil System in Gas Processing Plant
The strategies for the identification of potential energy saving in gas processing plant are as follows:
• The first is how to reduce energy losses in thermal oil system by maintaining the critical process parameter in
optimum value, minimizing heat losses in hot oil distribution system, and operating by well-trained personnel.
• The second principle is how to improve the specific energy consumption at hot oil generator as well as reboiler as
the end user of the process.
• The last principle is how to reduce the energy cost by selecting low fuel energy cost or waste heat utilization.

4. Optimized Thermal Oil Heater
𝐶 𝐻 + 𝑚 + 𝑂 + 3.76𝑁 →𝑚𝐶𝑂 + 𝐻 𝑂 + 3.76 𝑚 + 𝑁
TOH usually consist of Natural Draft or Forced Draft Type. Optimization in the
combustion system is very important for energy saving in TOH. The optimum
flue gas oxygen concentration depends on the load (duty), burner design, type
of fuel and burner performance.
Reducing oxygen while measuring CO gas allows the correct operating point to
be determined. The optimum excess air for a particular type of burner should
be known. It varies from one burner type to another and also depends on fuel
type.
Optimum excess air is the minimum excess air because it minimizes heat loss to
the flue gases, minimizes the cooling effect on the flame and improves heat
transfer. With less than minimum excess air, unburned fuel will appear in the
flue gas. Minimum excess air should be specified by the burner vendor and
should be verified during burner testing.
Fuel type Natural draft Forced draft
Fuel gas 15-20% 10-15%
Light fuel oil 20-25% 15-20%
Heavy fuel oil 25-30% 20-25%

5. Lesson learned in Optimized TOH
Figure shows the result of energy audit on three different gas
fuel thermal oil heaters in Indonesia. DMA, DMB and Crd are
thermal oil heaters with each capacity of 5.0 MWth, 5.8 MWth
and 1.2 MWth, respectively. High excess air in all thermal oil
heaters tend to lower in thermal efficiency. Thermal efficiency
improvement by optimizing the excess air setting can be
achieved by 1.3% for DMA, 1.8% for DMB and 0.65% for Crd.
70
72
74
76
78
80
82
84
86
0 1 2 3 4 5 6 7 8 9 10
Thermal
Efficiency
(%)
Excess Oxygen (%)
DM A DM B Crd
Hot oil
inlet
T
T
TT
T
T
FIC
T
T
FT
T
T
AT
T
T
PC
T
T
PT
Hot oil discharge
T
T
TIC
T
T
FIC
T
T
FT
Air
Air
Fuel
In reality, TOH is not always equipped with oxygen analyzer
for measuring the excess air. In the meantime, target of
hot oil discharged temperature cannot be achieved even
though the fuel valve has been fully opened.
The impact of high excess air is not only decreasing on
thermal efficiency, but also lowering on hot oil discharge
temperature.

6. Further Setting in The Process
Other case study of tuning on two thermal oil
heaters with each capacity of 5.8 MWth in a
local gas processing plant is shown in Fig.7.
Adjusting the excess air can reduce the fuel
flow on each TOH A and B with 0.23% and
1.03%, respectively. Furthermore, additional
setting on the hot oil flow can improve the
fuel saving more than only setting the excess
air. The improvement can be achieved on TOH
A and B are 3.17% and 1.92%, respectively.

7. Improving Specific Energy
Consumption in Amine Treating
Unit
Previous researchers have conducted many studies to optimize
energy use in amine stripper reboiler.
Choosing an efficient solvent shows a lower heat of absorption
The effect of the amine stripper configuration could reduce
energy requirement by 5-20%, and the loading of rich amine
and lean amine in amine stripper each has a relative effect on
heat duty [14].
Stripping columns should be operated at as high pressure as
possible to increase the reboiler temperature for optimum
CO2 and H2S stripping [15]. There are several control strategies
to optimize the amine regenerator performance. Several
process parameters can be considered to optimize amine
sweetening units for smooth operation and better H2S
absorption.
However, the energy requirement of amine regeneration is
related to the solvent use, reboiler temperature, solvent, rich
and lean amine loading, reboiler temperature, and the
structure of the amine stripper. These parameters directly or
indirectly impact H2S absorption, CO2 absorption, foaming,
amine degradation, corrosion rate, and reboiler duty [16].

8. Waste Heat Utilization
Preheated air combustion has been known
to offer simultaneous achievement on
energy savings as well as reduction of air
emission.
TOH usually uses normal ambient air as
combustion air. The one of energy saving
measure in thermal oil heater is by
preparing the combustion air be preheated
to high temperature using enthalpy
exchange from the exit gases of the
furnace section to the fresh incoming air.
Consequently, the air is preheated by heat
exchanging process from the hot
combustion gases to the incoming air. Air
preheated method has been commonly
used for the combustion of solid or low-
grade fuels.
Convective Radiant Radiant
Convective
Hot oil
inlet
Hot oil
inlet
Hot air
Fuel
Hot air
Ambient
Air Air Preheater
Hot oil
discharge
Hot oil
discharge
Flue gas Other waste
heat source
Air
Preheater
Fuel
Ambient
Air
Flue gas

9. A Case Study APH in TOH
• A Case study of air preheater on the existing natural gas fired heater with the
thermal capacity of 137 mm btu/hr (40.15 MWth)[18]
• The total heat losses consist of 2% from the heat loss to wall and 11% from the
dry flue gas losses. Waste heat recovery utilization for air preheating will improve
heat energy input to the fired heater and slightly reduce the heat energy from
the natural gas. Inlet air temperature increase from 30 oC to 220 oC using APH.
Portion of natural gas supply can be minimized from 98.6% to 91.6%, the other
meaning that the natural gas flow can be reduced compared without APH.
• Another study of air preheating methods into the existing fired heater units has
been investigated by the first and second law efficiencies. The thermal and exergy
efficiency increase from 63.4% to 71.7% and 49.4%, to 54.8%, respectively, with
implementation of APH [10]. Furthermore, the heat recovery and air preheating
methods lead to a substantial reduction in fuel consumption up to 7.4% followed
by decreasing heat loss and the irreversibility of the unit.

10. Energy balanced equation in a thermal oil heater refer to the first law is shown in Eq (2). Equation (3) shows
the implementation of APH will replace Qair with Q APH hot air. Q APH hot air is heated air as the result of heat
transferring from flue gas or other waste heat sources to inlet air in APH.
𝑄 +𝑄 = 𝑄 + 𝑄 + 𝑄 + 𝑄 + 𝑄 (2)
𝑄 +𝑄 = 𝑄 + 𝑄 + 𝑄 + 𝑄 + 𝑄 (3)
𝑄 = 𝑚 ℎ (4

11. Energy conservation in
Pumping System
Previous researchers have shown that energy saving of 30–50% could be achieved by proper selection of
components and system dimensioning in the pumping system [19,20].
Meanwhile, the strategy with parallel pumping systems, implementation of variable speed control of pumps
provides a better opportunity for energy savings instead of component selection and system dimensioning
[21,22].
In general, the energy conservation opportunities in pumping system are as follows [23]:
(a) replacing the existing inefficient pumps with energy efficient pumps,
(b) replacing the oversized components (pump, motor, and Variable Frequency Drive) with correct sized
components for efficient operation,
(c) optimizing the piping system by increasing pipe diameter and reducing the number of valves, elbows, and
fittings,
(d) operating the Variable Frequency Drive (VFD) in a frequency range of 35 Hz to 50 Hz to enhance the
efficiency of the drive,
(e) operating the pumps near best efficiency point,
(f) replacing the large capacity single pump unit with the parallel pumping system,
(g) minimizing the medium loss due to leakage and cracks by performing frequent maintenance.

12. Reducing energy losses in TO
distribution
Heat loss on thermal oil pipes occur by conduction,
convection, and thermal radiation. The heat loss from
thermal oil pipes needs to be minimized by insulation.
The thickness of the insulation material needs to be
optimized by considering some aspects, such as the costs
of the insulation material and energy, the heating system
efficiency, the lifetime and the current inflation and
discount rates. In case of the thermal insulation thickness
on a pipe increases, the heating transmission loads and
their costs (i.e., energy costs) decrease.
The thermal transmission loads from thermal oil heater
to reboiler in closed system are used as the input data for
an economic model to determine the various cost of the
insulation, included the present value of the energy
consumption, which is considered lost energy over the
lifetime of the system. Meanwhile, the insulation cost
increases with the amount of material used, as illustrated
in Fig [24].

13. Conclusion
This paper presents enhancement of energy efficiency of thermal oil system in gas processing plant.
Some energy audit experiences and other reviewed references in thermal oil system are presented
in this paper.
• Energy saving opportunities in thermal oil heater can be achieved by maintaining the air to fuel
ratio in optimum region. Reducing excess air in various thermal oil heaters have improved the
thermal efficiency with the range from 0.65 to 1.8%. Setting the excess air and parallel with hot
oil flow rate can achieve better fuel saving in thermal oil heater The benefit is not only to get the
best energy efficiency but also to accomplish the set point of hot oil discharge temperature. The
temperature and flow rate of hot oil entering reboiler have to fulfill as target design in order to
make more efficient in amine treating process. %. Further controlling the hot oil flow has
increased the thermal efficiency of the heater up to 3.1%.
• Improving energy intensity in amine treating unit means decreasing the heat demand to the
thermal oil heater.
• Furthermore, implementation of air preheating unit is also promising option in gas processing
plant. Waste heat recovery from fired heater itself or other waste heat source can potentially
improve in energy efficiency of thermal oil heater around 7%.

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