LNG VAPORIZATION STUDY
OREGON LNG IMPORT TERMINAL
~ Feasibility Study ~
Prepared for ~
Prepared by ~
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LNG
LNG
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CH·IV International
Baltimore Office
1341A Ashton Road
Hanover, MD 21076
410-691-9640
Houston Office
1221 McKinney, Suite 3325
Houston, TX 77010
713-964-6775
CH·IV International Document: TR-07902-000-002
Client Review Draft December 5, 2007
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OREGON LNG IMPORT TERMINAL
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TABLE OF CONTENTS
1
INTRODUCTION
4
2
BACKGROUND
4
2.1 Vaporizer System Overview
5
2.1.1 Vaporization System Requirements
5
2.1.2 Constraints and Assumptions Considered in Vaporization System Selection 5
2.1.3 Impact of Constraints and Assumptions on System Selection
3
7
AMBIENT AIR VAPORIZATION
9
3.1 Direct Ambient Air Vaporizers (AAVs)
9
3.1.1 Direct Natural Draft Ambient Air Vaporizers
11
3.1.2 Direct Forced Draft Ambient Air Vaporizers
13
3.2 Indirect Ambient Air Vaporizers
4
15
3.2.1 Ambient Air Heat Exchanger with Heat Transfer Fluid (AAV-HTF)
15
3.2.2 Smart Air ® Vaporizer
20
3.2.3 Other Indirect Ambient Air Heating Systems
21
3.2.4 Limitations on Use of Indirect Ambient Air Systems
21
3.3 EFFLUENTS DISCUSSION
22
3.4 IMPORT TERMINAL COMPATIBILITY
22
SUPPLEMENTARY HEATING
4.1 Submerged Combustion Vaporizers (SCVs)
24
25
4.1.1 Performance
26
4.1.2 Emissions and Effluents
26
4.1.3 Physical Characteristics
27
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4.1.4 Capital and Operating Costs
4.2 Gas Fired Heater with Heat Transfer Fluid (GFH–HTF)
28
4.2.1 Performance
29
4.2.2 Emissions and Effluents
29
4.2.3 Physical Characteristics
30
4.2.4 Capital and Operating Costs
30
4.3 IMPORT TERMINAL COMPATIBILITY
5
28
CONCLUSIONS AND RECOMMENDATIONS
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LIST OF FIGURES
Figure 3.1.1 – Schematic of Direct Ambient Air Vaporizer.......................................................10
Figure 3.1.1.1 – Direct Natural Draft Ambient Air Vaporizer in Operation ..............................11
Figure 3.1.2.1 – Direct Forced Draft Ambient Air Vaporizers without Shrouds .......................13
Figure 3.1.2.2 – Direct Forced Draft Ambient Air Vaporizers with Shrouds.............................14
Figure 3.2.1.3.1 – Dahej LNG Terminal.....................................................................................18
Figure 3.2.1.3.2 – Air Towers Under Construction at Freeport LNG Terminal.........................19
Figure 3.2.1.3 – STVs Under Construction at Freeport LNG Terminal .....................................19
Figure 4.1.1 Submerged Combustion Vaporizer .......................................................................25
Figure 4.1.3.1 – SCV Installation, 1.0 bscfd capacity ................................................................27
Figure 4.2.1 – Schematic of GFH–HTF Vaporization System...................................................29
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1
INTRODUCTION
The LNG Development Company, LLC, and the Oregon Pipeline Company, LLC
(collectively, Oregon LNG) proposes to construct and operate a liquefied natural gas (LNG)
import terminal (Import Terminal) on the East Bank Skipanon Peninsula (ESP) near the
confluence of the Skipanon and Columbia Rivers in Warrenton, Clatsop County, Oregon.
The proposed Oregon LNG Terminal and Oregon Pipeline (collectively, the Project)
consists of construction of a slip and berth for offloading LNG carriers (LNGCs), facilities
to receive and regasify LNG for transport to the United States (U.S.) natural gas
transmission grid, and approximately 120 miles of 36-inch-outside-diameter (OD) natural
gas pipeline (Pipeline), which in turn will interconnect with other natural gas pipelines,
including the interstate natural gas transmission system of Williams Northwest Pipeline
(Williams) at the Molalla Gate Station.
To minimize environmental concerns and maximize operating efficiency, the project design
basis requires that primary vaporization of LNG at the Import Terminal be achieved from
the heat available in ambient air. For seasonal conditions when ambient heat is unable to
meet design requirements, a fired heating system will supplement the ambient system. The
selection of a suitable vaporization system (a combination of ambient and fired heating) for
the Oregon LNG Import Terminal is therefore of principal importance. The selected system
will directly influence the capital cost, operational cost and environmental impact of the
Import Terminal. Additionally, the selection will also affect the regulatory requirements,
availability, operability and the general public perception of the Import Terminal.
The objective of this report is to select a suitable vaporization system for the Import
Terminal based on evaluation of various available vaporization systems. The selection is
based on the requirement to use heat available from ambient air to the extent possible, and
to determine the optimum method for providing supplementary heating at times when the
heat available from ambient air is insufficient to meet the sendout requirements. Different
ambient air vaporizers and supplemental (fired) heating systems are evaluated and compared
based on mechanical performance, capital and operating costs, emissions and effluent
discharge. Although no environmental modeling has been performed in the preparation of
this study, consideration has been given to emission and effluent discharge data provided by
equipment vendors in selecting the vaporization system.
2
BACKGROUND
Oregon LNG holds a long term sub-lease for approximately 96 acres of land located on the
East Skipanon Peninsula near the confluence of the Skipanon and Columbia Rivers in
Warrenton, Clatsop County, Oregon. The company proposes to build an LNG Import
Terminal on this parcel of land.
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The Import Terminal will provide a natural gas baseload sendout capacity of 1.0 billion
standard cubic feet per day (bscfd) and a peak sendout capacity of up to 1.5 bscfd. LNG
supplied to the Import Terminal via LNG carriers will be stored at -260°F in three 160,000
cubic meter above ground, full containment storage tanks. LNG vaporized into natural gas
will be transferred from the Import Terminal at 40°F via an approximately 117 mile long
sendout pipeline.
2.1
Vaporizer System Overview
The Import Terminal will use available heat from the ambient air for LNG
vaporization to the maximum extent possible, augmented, when necessary, with a
supplementary (fired) heat system to achieve the sendout temperature of 40°F.
Selection of a vaporization system therefore requires consideration of (1) the optimum
method for extracting heat from the ambient air, and (2) a compatible and efficient
system for providing the supplementary heat.
2.1.1
Vaporization System Requirements
The system requirements and constraints are summarized below. These
requirements are obtained from the Import Terminal Design Basis (document
07902-TS-000-002) and are as follows:
2.1.2
Import terminal location:
Pacific Northwest
Baseload sendout:
1.0 bscfd
Peak sendout:
Up to 1.5 bscfd
Gas sendout temperature:
40°F
Primary vaporization heat source:
Ambient Air
Constraints and Assumptions Considered in Vaporization System Selection
When considering the use of ambient air heat for vaporization of LNG under the
design requirements listed above, there are several key constraints that must be
considered. These constraints are described below.
•
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Ambient environmental conditions. Obviously, climate conditions are a
major factor in considering use of ambient air as a heat source for LNG
vaporization. The air temperature and relative humidity in particular have
a major impact on the performance of the ambient air vaporizers, and
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other factors such as solar radiation and wind can also impact performance
(more so for natural draft vaporizers). The table below shows the annual
average temperatures in Warrenton, Oregon between 2001 and 2005 (as
measured at the nearby Astoria Clatsop County Airport, COOP ID
# 350328). The data represents five years of average temperatures. As
shown in the table, the average annual temperature is 51.5°F, and the
average relative humidity is high. The temperatures vary seasonally, with
a winter temperature typically in the 30-40°F range and a summer
temperature typically in the 60-70°F range. The lowest temperature
recorded in this time period was 25°F; review of other weather data for the
region revealed an extreme low of 6°F over the past 30 years.
Table 2.1.2.1 Average Ambient Conditions in Warrenton Oregon
•
Year
2001
2002
2003
2004
2005
Average
Average
Temp
(°F)
50.8
51.0
52.2
51.8
51.5
51.5
Average
Humidity
(%)
84.0
81.2
82.1
85
82.9
83
Ambient air vaporizer approach temperature limitations. For heat
exchangers which operate by transferring heat between opposing flows of
hot and cold fluids, there are practical limitations in how closely the
heated fluid temperature can approach the temperature of the fluid
providing the heat. The difference between the inlet temperature of the
fluid providing the heat, and the outlet temperature of the fluid being
heated, is called the approach temperature. The achievable approach
temperature for a heat exchanger is a function of parameters such as the
available heat exchanger surface area, resistances in heat transfer between
the two fluids, and fluid flow rates. For this study, vendors were contacted
to determine the achievable approach temperatures for ambient air LNG
vaporizers. Approach temperatures typically vary from 20 to 40°F, and
worsen with running time due to heat transfer resistance resulting from
accumulation of ice on the vaporizer surfaces.
•
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Lack of available, local waste heat source. Currently there is no local
source of waste heat available for use for supplementary heating for this
Import Terminal. If a waste heat source (such as a power plant condenser
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or other industrial heat source) becomes available, the need for burning
fuel gas for supplementary heating could be reduced. However, this report
will assume that all supplementary heating will be provided by on-site,
fired heating equipment with no credit taken for waste heat sources.
2.1.3
•
Emissions and effluents. Of primary importance in selecting a suitable
vaporization system for this Import Terminal is the minimization of
environmental emissions and effluents. Ambient air vaporizers generate
no emissions; and they only generate ice and condensed water (possibly
with some entrained particulate matter) as effluents. However, fired
heating systems do generate emissions and effluents which generally
require treatment systems. The choice of supplementary heating system
will therefore consider the emissions and effluents associated with each
option.
•
Baseload and peak sendout. The vaporization system is designed to
sendout a baseload 1.0 bscfd and a peak of up to 1.5 bscfd. The peak
output can be provided with all spare equipment operating. The baseload
case must be provided with reliability, such that no credit can be taken for
standby equipment. Accordingly, the supplemental heating system will be
designed with spare equipment to ensure that in conjunction with the
ambient air vaporization system it can reliably provide sendout of 1.0
bscfd at 40°F. To achieve peak sendout of 1.5 bscfd, the spare equipment
in the supplementary heating system can be credited.
Impact of Constraints and Assumptions on System Selection
As pointed out in the previous section:
•
The design basis sendout temperature is 40°F;
•
The approach temperature for ambient air vaporizers varies considerably
depending on physical parameters and vaporizer run times, and is on the
order of 20 to 40°F;
•
The annual average ambient temperature is slightly over 50°F, and there
are periods during the year when the temperatures are lower.
To produce sendout gas at 40°F with an approach temperature on the order of 2040°F, the ambient temperatures would have to be no lower than 60°F and possibly
as high as 80°F. Since the weather data show that at many times during the year
the ambient temperature is below this level, the gas exiting the ambient air
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vaporizers will require supplemental heating to achieve the design basis sendout
temperature of 40°F .
Consequently, the supplemental heating system will be required to raise the gas
temperature exiting the ambient air system to the sendout temperature. For the
purposes of this evaluation, the ambient air system will be assumed to be able to
produce gas at 0°F, and the supplemental system will be designed to raise the gas
temperature to the sendout design basis temperature of 40°F.
The basis for selection of 0°F for the ambient air system is as follows:
•
It is assumed that the design and quantity of ambient air vaporizers will be
such that the average approach temperature will ensure exit gas
temperature of at least 0°F at times when the ambient air temperatures are
at the year round average (51.5°F) or higher. This requirement will be
included in the specifications provided to the vendor.
•
At times when the temperature is lower than the year round average, the
absolute content of water vapor in the ambient air will be relatively lower
than on hotter days. Accordingly, the vaporizers will accumulate frost and
ice at a slower rate, which will reduce the approach temperature. So, it is
appropriate to assume that the vaporization system should be able to
achieve 0°F under these conditions.
•
If the provided ambient air vaporization system is unable to heat gas to at
least 0°F due to accumulation of ice on the heat exchanger surfaces,
terminal operators can take action to remove the ice mechanically or by
other means. It is assumed that the terminal design and operating
procedures will account for this potential.
It is recognized that under extreme cold conditions, it may not be possible to
achieve 0°F gas exit temperature from the ambient air system. These events are
expected to be very rare. To ensure the baseload sendout can meet these
conditions, the supplementary heating system will include design margin.
Table 2.1.3.1 summarizes the proposed vaporization system design parameters for
the Import Terminal.
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Table 2.1.3.1 Ambient Air Vaporizer and Supplementary Heater System Design Parameters
Sendout
Capacity
(bscfd)
Average
Ambient
Temperature
(°F)
Assumed
Temperature at
Outlet of
Ambient Air
Vaporizers
Heat Provided
From Ambient
Air
(MMBtu/hr)
(°F)
1.5
51.5
0
751
Temperature
at Outlet of
Supplemental
Vaporizers
Minimum Heat
Required from
Supplemental
(°F)
(MMBtu/hr)
40
133
System
Having established that ambient air vaporizers in tandem with supplementary
heating systems are required for the Import Terminal, attention will now be
focused on the various ambient and supplementary fired systems – specifically,
the modes of operation, capital and operating costs and the emissions and
effluents associated with each.
3
AMBIENT AIR VAPORIZATION
Ambient air vaporization systems draw heat from the surrounding ambient air to vaporize
LNG. There are two primary methods of vaporization using heat from the ambient air: by
direct or indirect heat transfer into the LNG.
3.1
Direct Ambient Air Vaporizers (AAVs)
Direct AAVs transfer heat from the ambient air directly into the LNG through a heat
exchanger heat transfer surface. In typical Direct AAVs, the cryogenic liquid is
passed through a manifold that divides the flow into a number of vaporizer units where
a series of smaller flows are directed through individual heat transfer tubes. Each tube
has aluminum fins for increased heat exchange area and is in direct contact with the
ambient air. Figure 3.1.1 shows a schematic of a typical Direct AAV.
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Warm
Ambient Air
Natural Draft or Fan
Assisted
Cold Liquid
LNG
Natural Gas
Cool
Ambient Air
Figure 3.1.1 – Schematic of Direct Ambient Air Vaporizer
One disadvantage to the use of Direct AAVs is lack of experience with these units in
high volume vaporization of LNG. However, Direct AAVs have been used in liquid
nitrogen service (a fluid colder than LNG) for over fifty years.
While Direct AAVs are in operation, frost and/or ice will build up on the units due to
the proximity of the LNG to the ambient air. The longer a unit runs, the more frost
and/or ice builds, which gradually reduces the performance of the unit. Hence, Direct
AAV units need to be periodically shut down and de-iced.
De-icing becomes difficult when the ambient air temperature drops below freezing. In
this case, the system must be provided with another source of heat for de-icing, such as
electric heaters or water spray. At the proposed site, weather data shows that the
temperature rarely drops below freezing and then only for short periods of time.
Fortunately, during cold periods the available moisture in the air is relatively low,
minimizing the rate of ice buildup at these times. Experience from current users and
vendors (e.g., Thermax and Cryoquip Inc.) of Direct AAVs has shown that during
periods of extended cold weather, longer operating durations can be achieved by
running all the units simultaneously at a reduced rate while gradually increasing the
supplementary heat as frost continues to form on the vaporizer. The design of the
system will account for having adequate vaporization capacity and availability year-
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round taking into consideration downtime of a subset of the unit population for deicing.
It should be noted that although Direct AAVs can only heat gas up to a temperature
approaching the ambient temperature, the units can provide a high percentage of the
total heat load for vaporizing LNG. Per one vendor contacted, a Direct AAV
operating at arctic conditions of -80°F could provide over 50% of the total heat duty
needed to vaporize LNG.
There are two types of Direct AAVs – Natural Draft AAVs and Forced Draft AAVs.
3.1.1
Direct Natural Draft Ambient Air Vaporizers
Direct Natural Draft AAVs rely on wind and natural convective currents to move
air over the tubes and fins of the vaporizer unit. As warm air contacts the tubes
containing LNG, the air cools and becomes dense, causing it to flow downwards
to the bottom of the vaporizer unit. This causes warm ambient air from the
surroundings to be drawn through the top of the unit. Figure 3.1.1.1 illustrates a
Direct Natural Draft AAV in operation.
Figure 3.1.1.1 – Direct Natural Draft Ambient Air Vaporizer in Operation
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3.1.1.1 Performance
The outlet gas temperature of a Direct AAV is dependent not only on ambient
conditions but on other factors such as run time and amount of units in operation.
Consider a single AAV unit; at the onset of operation the temperature of the
outlet stream is nearly the same as the ambient temperature. As the run time
increases, the unit begins to frost and/or ice up, thus reducing the amount of heat
being transferred to the LNG. A significant amount of heat transfer is still
achieved, but the temperature of the outlet stream reduces as time passes and ice
accumulates. As more units come into operation, more surface area becomes
available for heat transfer. Per a vendor contracted for this study, it is estimated
that 12 basic trains (13 units/train) plus 6 duty cycle extra trains (that is, idle
vaporizers that are out of service undergoing de-icing while others operate)
would be required to vaporize 1.5 bscfd of LNG.
3.1.1.2 Emissions and Effluents
Cooling of the moist ambient air results in condensation of a large amount of
water vapor from the atmosphere. Some of this condensed water collects as frost
and/or ice on the tubes of each unit. Typically, the ice from the surface of each
unit melts and drains to a collection basin during the de-icing cycle. This water
is expected to have minor or no contamination and may be treated prior to
disposal or used within the Import Terminal. Another issue resulting from the
cooling of the ambient air is the formation of water vapor as “fog”, which can
create a visible cloud close to the Import Terminal.
3.1.1.3 Physical Characteristics
Per one vendor contacted for this study, typical Natural Draft AAVs that would
be used for this import terminal consist of vertical tube bundles 42-ft in length
with a plot area of 12-ft by 12-ft each. The vaporizers are elevated above grade
to prevent recirculation of cold dense air from the bottom of the unit back to the
inlet at the top of the unit. The total footprint of these vaporizers is therefore 320ft x 230-ft, or 73,600 ft2, assuming a 6-ft clearance between the estimated 236
units (18 trains, with 13 units/train) required for operation and duty cycle. Each
unit weighs approximately 52,000 lbs when dry and can withstand ice loading up
to an additional 60,000 lbs.
3.1.1.4 Capital and Operating Costs
Capital costs for the Natural Draft AAV arrangement for an LNG sendout
capacity of 1.5 bscfd have been estimated by Cryoquip Inc. to be $58 million
(vaporizers only). Operating costs on the other hand would be low. The power
input for these units is zero. There are no moving parts in the vaporizers and they
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are, for practical purposes, maintenance free. The only costs involved in
operation would be those required to handle the effluents from the vaporizers.
3.1.2
Direct Forced Draft Ambient Air Vaporizers
In Direct Forced Draft AAVs, airflow into the unit is controlled by fans installed on
top of the vaporizer. Each unit can be equipped with shrouds on each side to direct
airflow through the vaporizer. Direct forced draft vaporizers are approximately 1.7
times more effective than Natural Draft AAVs i.e., they move 1.7 times more air
across the tubes of the unit. Figures 3.1.2.1 and 3.1.2.2 show two types of Direct
Forced Draft Ambient Air vaporizers.
Figure 3.1.2.1 – Direct Forced Draft Ambient Air Vaporizers without Shrouds
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Figure 3.1.2.2 – Direct Forced Draft Ambient Air Vaporizers with Shrouds
3.1.2.1 Performance
Since the airflow through the forced draft units is higher than for natural draft
units, fewer forced draft units will be required to achieve the same duty. Per one
vendor contacted for this study, it is estimated that 10 basic trains (10 units/train)
plus 5 duty cycle extra trains would be required for the vaporization of 1.5 bscfd.
3.1.2.2 Emissions and Effluents
Emissions and effluents for forced draft units are similar to the natural draft units
as described in 3.1.1.2, except that with Forced Draft AAVs the formation of fog
is diminished by the forced airflow (from the fans on top of each unit) around the
tubes. There is also more ice formed in Forced Draft units because the increased
air flow over the tubes increases the rate of water condensation and consequently
the rate of ice formation. The shrouds around the tube bundles impede the
amount of radiant heat reaching the ice forming on the tubes, which can increase
the ice buildup rate.
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3.1.2.3 Physical Characteristics
Physical requirements are similar to the Natural Draft AAVs arrangement, except
that fewer forced draft units are needed. Assuming 150 units and 6-ft spacing
between each unit and each train, the total land area needed for all the vaporizers
is estimated at 170-ft x 260-ft or 44,200 ft2. The weights of these units are
comparable to the natural draft units, with a small addition due to the weight of
the shrouds and fans.
3.1.2.4 Capital and Operating Costs
The total capital costs for Forced Ambient Air vaporizers has been estimated at
$56 million (vaporizers only) by Cryoquip Inc. Operating costs for Forced Draft
AAVs would be higher than natural draft AAVs due to the electric power needed
for the fans; each unit requires power to the fans on the order of 60 HP (about 45
kW). With 15 trains in constant operation (units in the de-icing cycle would also
have the fans on) the power requirement would be on the order of 9,000 HP or
6.7 mW.
3.2
Indirect Ambient Air Vaporizers
Indirect vaporizers operate by transferring heat from ambient air to an intermediate
fluid which in turn transfers heat to LNG through a separate heat exchanger. The
different arrangements of Indirect Ambient Air Vaporizers are described below.
3.2.1
Ambient Air Heat Exchanger with Heat Transfer Fluid (AAV-HTF)
This type of vaporization system consists of Shell and Tube Heat Exchangers,
Fin-fan Air Heaters or Reverse Cooling Towers and a Heat Transfer Fluid loop.
Fin-Fan Air Heaters are used to transfer heat from ambient air into the HTF,
which is then sent to the LNG shell and tube vaporizer. The cooled HTF flows
into a surge tank and is then pumped back to the Air Heaters. Schematics of the
different vaporization processes are shown below in Figures 3.2.1.1 and 3.2.1.2.
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WARM HTF
AIR HEATERS
LNG
Pipeline Gas
SHELL AND TUBE
VAPORIZER
HTF
SURGE TANK
COLD HTF
HTF PUMP
Figure 3.2.1.1 – Schematic of AAV-HTF System Using Air Heat Exchangers
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LNG
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Figure 3.2.1.2 – Schematic of AAV-HTF System Using Reverse Cooling Tower
Although the main heat source for this vaporization arrangement is the heat
contained in the warm ambient air, supplemental heating is also required to
maintain capacity and delivery temperature when the ambient air temperature
drops below a nominal value.
The vaporization system using fin-fan heat exchangers shown in Figure 3.2.1.1 is
in operation at the Dahej LNG terminal in India and is being installed at the Lake
Charles LNG terminal in Louisiana. The vaporization system using Reverse
Cooling Towers shown in Figure 3.2.1.2 is being used at the Freeport LNG
project.
3.2.1.1 Performance
Typical indirect air heating systems in operation in the hot areas like India and
the Gulf of Mexico area are capable of delivering about 90% of the annual heat
load. In more temperate climatic regions like Oregon, that capability is reduced
to between 55-60%. This availability is also applicable to Fin Fan Air Heat
exchangers. These vaporization systems also have a significant electrical load.
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3.2.1.2 Emissions and Effluents
Water produced from condensation of water vapor from the surrounding air must
be continuously discharged and safely discarded. For Reverse Cooling Tower
systems, the circulating water stream is likely to require chemical treatment and
the blowdown needs to be appropriately handled.
3.2.1.3 Physical Characteristics
The AAV-HTF system presents a significant demand on its supporting
infrastructure. A Google Earth® satellite photo of the Dahej terminal is shown in
Figure 3.2.1.3.1. The components shown on the right side of the photo outline
the air heat exchanger arrangements for the vaporization of 1.0 bscfd, which is
the baseload case for the Oregon LNG Import Terminal. Figures 3.2.1.3.2 and
3.2.1.3.3 illustrate Air Towers and Shell and Tube Vaporizers (STVs, used for
supplemental heating when the heat available from ambient air is insufficient)
under construction at the Freeport LNG terminal. The heating towers require a
large plot area.
Figure 3.2.1.3.1 – Dahej LNG Terminal
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Figure 3.2.1.3.2 – Air Towers Under Construction at Freeport LNG Terminal
Figure 3.2.1.3 – STVs Under Construction at Freeport LNG Terminal
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3.2.1.4 Capital and Operating Costs
Shell and tube heat exchangers rated for high sendout pressures (over 1000 psi)
and capacities (approximately 100 to 150 mmscfd) are estimated at roughly
$500,000 a unit. The Oregon LNG Import Terminal would require at least 10 of
these units for a maximum sendout capacity of 1.5 bscfd. Also, as stated earlier,
Reverse Cooling Towers are large structures and would require significant capital
investment for construction and operation. Power consumption costs due to
ancillary equipment such as fans and pumps should also be taken into account,
making this vaporization system cost intensive.
3.2.2
Smart Air ® Vaporizer
The Smart Air® vaporization system is similar to the AAV-HTF system discussed
in section 3.2.1, except that the system uses Potassium Formate (KF) as the heat
transfer fluid. The system consists of Air Heaters, a Surge Tank, Pumps, and
Shell and Tube LNG vaporizers. The Air Heaters transfer heat from the warm
ambient air into cool KF fluid from the Shell and Tube LNG Vaporizer. The
warmed KF fluid is then sent to the Surge Tank. KF fluid is pumped from the
Surge Tank back to the Shell and Tube vaporizers where it provides heat to the
LNG, is cooled, and then sent back to the Air Heaters.
The Air Heaters used in the Smart Air® vaporization system are proprietary to
Mustang Engineering. Each Air Heater contains layers of finned tubes and has
fans forcing the ambient air from the surroundings to flow through the top of the
unit downwards, over the tube bundle. The Air Heaters are elevated above grade
to prevent recirculation of cold dense air from the bottom of the unit to the fan
inlet.
As with other ambient air vaporization systems, supplementary heat will be
required when design ambient conditions cannot be met.
3.2.2.1 Performance
Promoters of the Smart Air® Vaporization system claim the system would be able
to provide 65% of the annual heat duty for the Oregon area. As this vaporization
system is yet to be installed in a region of similar climate as Oregon, this claim
remains unconfirmed. Smart Air® vaporization systems also have significant
electric power demands for the ancillary equipment including fans for air heaters
and pumps. A system rated for 1.5 bscfd would require about 9000 HP.
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3.2.2.2 Emissions and Effluents
Cold, condensed water from the atmosphere continuously forms on the surface of
the tubes containing cold KF fluid. The water falls off the tubes exiting from the
bottom of the air heater with the flow of cooled air. The water can be collected in
a basin below the air heaters and utilized in the plant, treated and used for potable
water or discarded. The condensed water is clean, freshwater and does not
require significant treatment and can be discarded easily. Estimated waste water
flow rate for a system rated at 1.5 bcsfd is 1000 gpm.
3.2.2.3 Physical Characteristics
For a sendout capacity of 1.0 bscfd, the LNG Smart Air® vaporization system
would require a total surface area of 27,240 ft2. The vaporization system at
Oregon will be sized for a total capacity of 1.5 bscfd; hence it is reasonable to
assume that the acreage needed would be approximately 40,860 ft2. Each threefan Air Heater unit measures 14ft wide, 60ft long and 40ft high.
3.2.2.4 Capital and Operating Costs
The total cost for a Smart Air® Vaporization system with a 1.5 bscfd capacity is
estimated to be $80 million. Extra costs will also be incurred due to treatment
and handling of wastewater produced by the Air Heaters and electrical power
consumption from the fans for the heaters.
3.2.3
Other Indirect Ambient Air Heating Systems
Other Ambient Air vaporization systems exist but are not discussed here because
they either cannot be incorporated into the Oregon LNG Import Terminal design
or they are not proven technologies. An example of such a vaporization system is
the Heat Integrated Ambient Air Vaporization (HIAAV). HIAAV systems involve
the use of Waste Heat recovery units installed in combination with gas turbines
which the Oregon LNG Import Terminal design does not include.
3.2.4
Limitations on Use of Indirect Ambient Air Systems
Per discussions with vendors, indirect systems work best when air temperatures
are above 70°F; when the ambient air temperature drops below that value, the heat
available from the ambient air is insufficient and supplemental heat must be added
to the HTF. When the air temperatures drop below about 50°F, heat transfer from
the ambient air is ineffective and essentially all vaporization heat must be
provided from supplement heat sources. Note that the year-round average
temperature at the terminal site is on the order of 50°F, so these indirect methods
would need to be backed up by supplemental systems operating at 100% of the required
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duty for vaporization for much of the year. That is, if an Indirect Ambient Air
Vaporization were to be used at this terminal, two different, full capacity
vaporization systems would need to be installed.
3.3
EFFLUENTS DISCUSSION
One of the advantages of using ambient air vaporizers is that they do not produce any
emissions. However all ambient air vaporization methods create effluents that need to
be properly handled. In Direct Ambient Air Vaporizers, frost and/or ice builds up on
the tube bundles of each unit as a result of the freezing of condensed water from the
ambient air that forms on the tubes. During the de-icing cycle all the ice falls off the
unit and has to be properly discarded.
Indirect Ambient Air Vaporizations systems also generate condensed water as
effluent. However, since air does not come in direct contact with a heat transfer
surfaces containing cryogenic fluid, there is little or no ice formation.
For each type of vaporizer, the rate of amount of water formation (as ice or
condensate) can be as high as 1000 gpm (liquid water equivalent) for a 1.5 bscfd
terminal. The terminal design needs to address treatment of this effluent.
3.4
IMPORT TERMINAL COMPATIBILITY
Table3.4.1 shows a comparison of the ambient air vaporization systems discussed in
Section 3 of this report.
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Table 3.4.1 –Comparison of Air Vaporization Systems
Direct Ambient Air
Vaporization
Natural Draft
Indirect Ambient Air Vaporization*1
Forced Draft
AAV-HTF
(Air Heat
Exchangers)
AAV-HTF
(Reverse
Cooling Towers)
Smart Air®
Provides large fraction of total heat duty during
hot ambient conditions;
Ambient
Temperature
Operating
Range
Provides large fraction of
total heat duty at all expected
ambient temperatures
Estimated
Capital Cost
$152 million
$147 million
$98 million
$100 million
$95 million
Land Usage
73,600 ft2
44,200 ft2
167,000 ft2
100,000 ft2
40,860 ft2
Power Usage
for AAVs
None
High (fans)
High (fans
and pumps)
Moderate
(pumps)
High (fans
and pumps)
Water
Water
Water
Effluents
Water and ice Water and ice
Provides little or no heat duty at times when
temperatures drop below 50°F
In summary:
• During much of the year the ambient air temperature at the site is on the order of
50°F or lower. Under these conditions, indirect systems provide little or no heat.
Accordingly, for these systems, a 100% capacity supplemental system would be
required in order to achieve sendout during cold periods. This would increase the
capital cost and land area needed for the Import Terminal, and increase the yearly
emissions from the terminal. For these reasons, indirect systems are considered
inappropriate for this facility.
• Direct AAVs would provide much of the heat duty but require supplemental heat
during cold periods.
• Of the two types of direct AAVs, fewer forced draft AAVs are needed than natural
draft AAVs; thus, significant land area can be saved if forced draft AAVs are used.
However, natural draft AAVs do not require electric power whereas forced draft
AAVs use electrically powered fans.
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Therefore, the Direct Forced Draft Ambient Air vaporization system will be the most
suitable option for the Oregon LNG Import Terminal. It is estimated that 10 basic
trains (10 units per train) plus 5 duty cycle extras can provide the entire heat load
expected from the Direct Forced Draft AAVs for the peak sendout capacity of 1.5
bscfd. On occasions when the ambient conditions cannot provide sufficient heat,
supplemental heat would be provided, as discussed in the next section.
4
SUPPLEMENTARY HEATING
When the ambient temperature is not warm enough to raise the temperature of the vaporized
LNG to 40°F, supplement heating must be provided to reach this design basis sendout
temperature. Figure 4.1 illustrates how the supplemental heating system would be integrated
with the Ambient Air Vaporization system at the Oregon LNG Import Terminal. The
minimum amount of heat needed from the supplemental system has been determined section
2.1.3 to be 133 MMBtu/hr. To be conservative, the supplemental vaporization system will
be sized for 180 MMBtu/hr which provides 35% extra capacity.
VAPORIZED LNG @
<40°F
Natural Gas
@ 40°F
Sendout
Station
VAPORIZED LNG @
>40°F
Supplemental
Gas Fired
Vaporizer
COLD LNG
FROM TANK
Ambient Air
Vaporizer
Figure 4.1 – Overall Schematic of Vaporization System
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As illustrated above, cold LNG from the storage tanks is pumped to the AAVs which
vaporize the LNG. If the AAVs do not provide sufficient heat to raise the temperature to
40°F, a side stream of the gas exiting the ambient air vaporizers is sent through the
supplemental heating system and warmed to a temperature greater than 40°F. The warm
stream is blended with the cooler, vaporized LNG from the AAVs and sent to the metering
station at 40°F.
Gas fired heating systems are proven and effective methods of providing heat for vaporizing
LNG. They can also operate largely unaffected by surrounding climatic conditions.
However, these systems consume fuel and generate emissions. Two gas fired heating system
options were considered for Oregon LNG and are described below:
4.1
Submerged Combustion Vaporizers (SCVs)
SCVs are designed to use fuel gas or low pressure boiloff gas from the terminal. High
pressure LNG flows through a stainless steel tube bundle that is submerged in a water
bath heated with exhaust gases generated from a combustion burner. The water
transfers the heat from the combustion process to the LNG. The SCV alternative offers
simplicity and has become the vaporization choice for many new and existing U.S.
regasification terminals. Figure 4.1.1 is a schematic for the SCV process.
Figure 4.1.1 Submerged Combustion Vaporizer
The hot exhaust gases from this combustion are sparged into the water bath and create
a relatively low temperature (typically in the range of 50° to 60° F) thermally stable
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heat source for the vaporization coils. The vaporized LNG exits the coils at pipeline
pressure and design basis temperature for downstream transmission.
4.1.1
Performance
SCVs have very high thermal efficiencies (above 95%) because the combustion
products are bubbled directly into the water bath hence all the available heat is
transferred directly to the water. This includes the latent heat of condensation of water
vapor in the exhaust gas which also condenses in the water bath. Gas outlet
temperatures for SCVs range from 35°F to 60°F. Since the water bath is at high
thermal capacity, stable operation is generally achievable, even for sudden start-ups,
shutdowns or deviations in load. Electric power is also required to run the combustion
air blower and the water circulation pumps.
4.1.2
Emissions and Effluents
Due to the combustion process NOx, CO and other emissions are produced when
the SCVs are in operation. Table 4.1.2.1 contains the emissions from a typical
SCV unit.
Table 4.1.2.1 – Emissions from a Typical SCV Unit (rated at 94.2 MMBtu/hr)
Pollutant
Emissions (pounds per
million Btu @ 3% O2)
NOx
<0.0345
CO
<0.025
VOC
<0.003
Particulate Matter (PM 10) is also emitted at a rate of 0.0015 lb/MMBtu.
Reducing these emissions (especially the NOx) will require the use of a selective
catalytic reactor (SCR). SCRs are expensive and do not operate efficiently with
SCVs. SCR catalysts can be “poisoned” or “fouled” during SCV operation due to
contact with potassium or sodium salts used in pH neutralization of the water
bath. Optimum temperatures for an SCR reaction range from 650-750°C and may
go as high as 1000°C depending on what catalyst is used. SCVs cannot generate
exhaust gas at these temperatures and hence SCV exhaust cannot be treated via
SCRs without costly re-heating of the exhaust gas.
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During SCV operation the water in the bath becomes acidic as it absorbs
combustion products. The pH of the water bath is monitored and controlled by
introducing alkaline chemicals such as caustic soda or sodium carbonate. It is
important to maintain a relatively neutral pH level (between 6 and 7) in the water
bath. During the combustion process, waste water is also produced and must be
treated before disposal. For a single SCV unit rated for approximately 94
MMBtu/hr (which is about 50% of the maximum supplemental heat needed) there
is a water overflow rate of about 15.5gpm. Hence it is expected that an SCV
system installed at the import terminal would produce about 30 gpm of waste
water.
4.1.3
Physical Characteristics
An SCV unit with a vaporization capacity ranging from 150-200 mmscfd (typical
size of a unit) will have a minimum footprint of 408 ft2. Stack heights can vary
based on owner requirements. The layout of SCVs can be seen in Figure 4.1.3.1.
Figure 4.1.3.1 – SCV Installation, 1.0 bscfd capacity
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4.1.4
Capital and Operating Costs
SCV units usually have a vaporization capacity range of 150-200 mmscfd. Each
unit costs approximately $2 million. Two units would be needed for the
supplemental heat system at Oregon LNG. Hence a total capital cost (vaporizers
only) of $4 million would be required. This amount takes into account the cost of
ancillary equipment such as the air blower, circulation pump, fuel gas heater,
controls and associated piping. This cost does not include an SCR unit. The
greatest disadvantage of purchasing SCVs is the operating costs. Current
technology is such that fuel consumption is in the range of 1.3% to 1.5% of
throughput. It is important to note that for the Oregon terminal throughput does
not refer to the full sendout capacity of the terminal, as the supplemental system is
only designed to heat the gas exiting the ambient air vaporizers, which has already
been heated. Instead, it refers to the equivalent amount of LNG (at -260°F) that is
vaporized by 180MMBtu/hr, i.e., approximately 300 mmscfd. The annual power
consumption costs for the air blowers must also be considered due to the motor
size and required excess air. The estimated annual operating costs for two SCV
units running at their maximum output (i.e., a total of 180 MMbtu/hr) is $6
million.
4.2
Gas Fired Heater with Heat Transfer Fluid (GFH–HTF)
The GFH–HTF vaporization systems involve the use of gas fired heaters as the
primary source of heat to vaporize LNG. Heat is supplied to shell and tube LNG
vaporizers through a closed circuit with a heat transfer fluid, usually a mixture of
water and ethylene glycol (WEG), as the heat transfer fluid. A schematic of the
system is shown in Figure 4.2.1. Gas fired heaters heat the HTF which is then sent
directly to the LNG vaporizer. The cooled HTF is collected in a surge tank and
pumped back to the Gas Fired heaters. A system very similar to that shown is
used on multiple vaporizer systems at the Distrigas LNG Terminal in Everett,
MA.
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Figure 4.2.1 – Schematic of GFH–HTF Vaporization System
4.2.1
Performance
The fired heaters used in this vaporization system are capable of heating WEG to
temperatures up to 200°F. Based on the proposed operation of the vaporization
system at the Oregon LNG Import Terminal, the capability of heating up a side
stream of the vaporized LNG to temperatures much greater than 40°F is
necessary. The GFH–HTF system has this capability. Gas fired heaters used in
this system burn approximately 1.8% - 2.2% of throughput1 and have efficiencies
of approximately 83%. The system will also have a significant electrical load
from heater forced draft fans, HTF pumps and other ancillary equipment.
4.2.2
Emissions and Effluents
Typical air emissions data for the burner associated with a Gas Fired Heater with
a heat duty of 60 MMBtu/hr are presented in Table 4.2.2.1.
1 Note that the throughput in this case has been defined in section 4.1.4
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Table 4.2.2.1 – Air Emissions from Gas Fired Heater
Pollutant
Emissions (pounds per
million Btu @ 3% O2)
NOx
<0.013
CO
<0.025
VOC
<0.003
It should be noted that Gas Fired Heaters are very compatible with SCRs due to
the high temperature of the exhaust. Hence, SCRs work very efficiently when
installed on Gas Fired Heaters and are capable of significantly reducing NOx and
CO emissions rates.
4.2.3
Physical Characteristics
The GFH–HTF system presents a minimal vaporizer footprint with the HTF
pumps and heaters located nearby typically in a “boiler house.” Footprints for Gas
Fired Heaters vary according to the size of the heaters. Next to the SCV, the
STV-GF requires the least land area due to minimal system components. Vertical
shell and tube heat exchangers used in this application have an approximate outer
diameter of about 42 inches. Multiple exchangers will be needed for the
supplementary heating system.
4.2.4
Capital and Operating Costs
Shell and tube heat exchangers used in this system are estimated to cost $500,000
a unit. The Oregon LNG Import Terminal will require at least three heat
exchangers. Gas fired heaters rated at 60 MMBtu/hr with an SCR and associated
ancillary equipment i.e., surge tank, pumps etc. can cost up to $1 million per unit.
Estimated total capital costs for this system is $4.5 million. Operating costs will
comprise mainly of power and fuel consumption charges for the unit. Power
consumption from the system would be mostly from horsepower requirements for
the heater forced draft fans pumps.
4.3
IMPORT TERMINAL COMPATIBILITY
SCVs are not considered acceptable for supplemental heating for this terminal since
they are not effective at heating gas to high temperatures (which is needed for
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blending purposes). In addition, the emissions from SCVs cannot be controlled using
normal SCR technology.
Gas fired heaters with a heat transfer fluid loop and shell and tube heat exchangers
offer a more flexible and efficient option. The heaters and heat exchangers can be
used to raise the natural gas temperatures to high values to aid in blending to reach the
40°F sendout temperature. The number and capacity of Gas Fired Heaters can be
optimized to allow large turn down ratios. Gas fired heaters also work very well with
SCRs to reduce emissions rates. Shell and tube heat exchangers are versatile, simple
and widely used components, and can be easily customized to meet various operations
requirements.
5
CONCLUSIONS AND RECOMMENDATIONS
LNG vaporization at the Oregon LNG Import Terminal will occur in two stages: (1) an
ambient air vaporization system will provide much of the heat needed for vaporization, and
(2) a supplemental heating system will provide the remaining heat needed when ambient
conditions are not sufficient to reach the design sendout temperature.
At Oregon, the year-round temperature is such that indirect ambient air vaporization
systems will not be effective during much of the year. Use of indirect systems would
therefore require installation of 100% capacity backup fired heating systems. This would
result in large capital costs and generation of more annual emissions than a system using
direct AAVs. Accordingly, direct AAVs are deemed to be the most appropriate method for
extracting heat from the ambient air at this terminal.
Of the two types of direct AAVs, forced draft AAVs are recommended over natural draft
AAVs at this time due to the reduced capital costs and land area.
One disadvantage to using Forced Draft AAVs is its lack of a proven track record in high
volume LNG vaporization service. However, AAVs have been effectively used for years to
vaporize liquid nitrogen which is a cryogenic fluid colder than LNG.
Of the two options considered for the supplementary heating system, the Gas Fired Heaters
with Heat Transfer Fluid (GFH-HTF) system is considered a better choice than Submerged
Combustion Vaporizers (SCV). The GTF-HTF works well with a Selective Catalytic
Reduction system (SCR) hence its emissions rates can be efficiently and significantly
reduced, unlike SCV units. Also SCVs are not efficient at delivering natural gas at the high
temperatures needed for downstream blending with cold gas for achieving the design
sendout temperature, thus ruling out their use for supplementary heating at this terminal.
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In summary, CH·IV recommends that Oregon LNG use Direct Forced Draft Ambient Air
Vaporizers for its primary vaporization system and a GFH-HTF as a supplemental heating
system. This combination presents the most effective option for LNG vaporization at the
Import Terminal.
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