1. Installing Vapor Recovery Units to Reduce Methane Losses
Lessons Learned
from Natural Gas STAR
Producers Technology Transfer Workshop
Devon Energy and
EPA’s Natural Gas STAR Program
Casper, Wyoming
August 30, 2005

2. Vapor Recovery Units: Agenda
Methane Losses
Methane Savings
Is Recovery Profitable?
Industry Experience
Discussion Questions

3. Methane Losses from Storage Tanks
Storage tanks are responsible for 6% of methane emissions in natural gas and oil production sector
96% of tank losses occur from tanks without vapor recovery
Other Sources
21 Bcf
Storage Tank
Venting
9 Bcf
Pneumatic Devices
61 Bcf
Meters and
Pipeline Leaks
10 Bcf
The numbers here are from the 2003 inventory.
.425 Bcf from tanks with control devices / ( Bcf) = 4% of tank emissions are from tanks with control devices (this is from 2003 petroleum and gas inventories)
Gas Engine Exhaust
12 Bcf
Dehydrators
and Pumps
17 Bcf
Well Venting
and Flaring
18 Bcf
Inventory of U.S. Greenhouse Gas Emissions and Sinks

4. Sources of Methane Losses
9 Bcf methane lost from storage tanks each year from producers*
Flash losses - occur when crude is transferred from a gas-oil separator at higher pressure to an atmospheric pressure storage tank
Working losses - occur when crude levels change and when crude in tank is agitated
Standing losses - occur with daily and seasonal temperature and pressure changes
7.877 Bcf from tanks, 2003 petroleum inventory (this takes into account an assumption that 29% have control devices)
2.26 Bcf from tanks w/o control devices, 2003 gas inventory
0.45 Bcf from tanks w/ control devices, 2003 gas inventory
* Inventory of U.S. Greenhouse Gas Emissions and Sinks

5. Methane Savings: Vapor Recovery Units
Capture up to 95% of hydrocarbon vapors vented from tanks
Recovered vapors have higher Btu content than pipeline quality natural gas
Recovered vapors are more valuable than natural gas and have multiple uses
Re-inject into sales pipeline
Use as on-site fuel
Send to processing plants for recovering NGLs
Vapor Recovery Units are of great value because they are able to capture up to 95 percent of the hydrocarbon vapors that accumulate in storage tanks.
These vapors usually have a higher Btu content than pipeline quality natural gas. The higher Btu content is the result of a natural refining process in which a lower pressure on the liquid crude allows some more complex hydrocarbon molecules to escape from the liquid and exist as components of the natural gas.
The higher Btu content of these vapors can be extracted in the form of liquids and sold as separate products (such as propane, butane, ethane, etc.). The value of these liquids, in addition to the value of the gas, depends on the demand for the specific product, but is generally more valuable than methane alone.

6. Types of Vapor Recovery Units
Conventional vapor recovery units (VRUs)
Use rotary compressor to suck vapors out of atmospheric pressure storage tanks
Require electrical power or engine
Venturi ejector vapor recovery units (EVRUTM) or Vapor Jet
Use Venturi jet ejectors in place of rotary compressors
Do not contain any moving parts
EVRUTM requires source of high pressure gas and intermediate pressure system
Vapor Jet requires high pressure water motive

7. Standard Vapor Recovery Unit
Control
Pilot
Suction
Line
Vent Line
Back Pressure
Valve
Crude Oil
Stock
Tank(s)
Electric
Control
Panel
Suction
Scrubber
Bypass
Valve
Gas
This graph illustrates a VRU installed on a single crude oil storage tank (multiple tank installations are also common).
Hydrocarbon vapors are drawn out of the storage (stock) tank under low pressure, typically between four ounces and two psi, and are first piped to a separator (suction scrubber) to collect any liquids that condense out.
The liquids are usually recycled back to the storage tank.
From the separator, the vapors flow through a compressor that provides the low pressure suction for the VRU system. (To prevent the creation of a vacuum in the top of a tank when oil is withdrawn and the oil level drops, VRUs are equipped with a control pilot to shut down the compressor and permit the back flow of vapors into the tank.)
The vapors are then metered and removed from the VRU system for pipeline sale or on-site fuel supply.
Gas Sales
Meter Run
Check Valve
Liquid
Transfer Pump
Condensate
Return
Electric Driven
Rotary Compressor
Sales
Source: Evans & Nelson (1968)

8. Vapor Recovery Installations

9. Vapor Recovery Installations

10. Vapor Recovery Installations

11. Vapor Recovery Installations

12. Vapor Recovery Installations

13. Vapor Recovery Installations

14. Vapor Recovery Installations

15. Venturi Jet Ejector* Temp Indicator Pressure Indicator High-PressureTI PI TI
High-Pressure
Motive Gas
(~850 psig)
Discharge
Gas
(~40 psia) TI
Flow Safety Valve PI
EVRUTM Suction Pressure
(-0.05 to 0 psig)
The pressure readings shown are for a specific example.
Low-Pressure Vent Gas from Tanks
(0.10 to 0.30 psig)
*Patented by COMM Engineering

16. Vapor Recovery with Ejector
Gas to Sales
@ 1000 psig
Compressor
6,200 Mcf/d
Gas
281 Mcf/d
Net Recovery
(19 Mcf/d Incr.fuel)
900 Mcf/d
5,000 Mcf/d Gas
5,000 Bbl/d Oil
Ejector
40 psig
LP Separator
Ratio Motive / Vent = 3
= 900/300
300 Mcf/d Gas
Oil & Gas Well
Oil
Crude Oil Stock Tank
Oil to Sales

17. Vapor Jet System*
The pressure readings shown are for a specific example.
*Patented by Hy-Bon Engineering

18. Vapor Jet System*
The pressure readings shown are for a specific example.
Utilizes produced water in closed loop system to effect gas gathering from tanks
Small centrifugal pump forces water into Venturi jet, creating vacuum effect
Limited to gas volumes of 77 Mcfd and discharge pressure of 40 psig
*Patented by Hy-Bon Engineering

19. Criteria for Vapor Recovery Unit Locations
Steady source and sufficient quantity of losses
Crude oil stock tank
Flash tank, heater/treater, water skimmer vents
Gas pneumatic controllers and pumps
Outlet for recovered gas
Access to low pressure gas pipeline, compressor suction or on-site fuel system
Tank batteries not subject to air regulations
The installation of a VRU can have a two-fold benefit:
It can be a profitable investment for the producer; and
By reducing hazardous air pollutants (HAPs) below specified action levels, the investor can avoid the need to comply with certain state and federal regulations.

20. Quantify Volume of Losses
Estimate losses from chart based on oil characteristics, pressure and temperature at each location (± 50%)
Estimate emissions using the E&P Tank Model (± 20%)
Measure losses using recording manometer and well tester or ultrasonic meter over several cycles (± 5%)
This is the best approach for facility design
Of the first two methods, using the chart (see next slide) is quicker and as accurate as direct measurement since it was designed using actual field data.
The E&P Tank model was developed by the American Petroleum Institute and the Gas Research Institute to give a greater magnitude of accuracy by computerizing the mathematical calculations from the field data and avoiding interpretation problems associated with the chart.

21. Estimated Volume of Tank Vapors
110
100 90 80
40° API and Over 70
Vapor Vented from Tanks- cf/Bbl - GOR 60
30° API to 39° API 50 40
Under 30° API 30 20 10 10 20 30 40 50 60 70 80
Pressure of Vessel Dumping to Tank (Psig)

22. What is the Recovered Gas Worth?
Value depends on Btu content of gas
Value depends on how gas is used
On-site fuel - valued in terms of fuel that is replaced
Natural gas pipeline - measured by the higher price for rich (higher Btu) gas
Gas processing plant - measured by value of NGLs and methane, which can be separated
The use of recovered gas as an on-site fuel can offset the retail cost of fuel and the cost of transportation to the site.
Natural gas is now sold by the energy content (Btu), not volume (Mcf). Rich gas demands a higher price from both pipelines and processing plants.

23. Value of Recovered Gas Gross revenue per year = (Q x P x 365) + NGL
Q = Rate of vapor recovery (Mcfd)
P = Price of natural gas
NGL = Value of natural gas liquids
As previously stated, VRUs can recover approximately 95 percent of accumulated hydrocarbon vapors. Thus, when calculating the value of recovered gas it is critical to keep in mind that the rate of vapor recovery (Q) is equal to 95 percent of estimated total gas losses.

24. Value of NGLs

25. Cost of a Conventional VRU

26. Is Recovery Profitable?

27. Top Gas STAR Partners for VRUs
Top five companies for emissions reductions using VRUs in 2003
Company
2003 Annual Reductions (Mcf)
Partner 1
1,333,484
Partner 2
962,078
Partner 3
661,381
Partner 4
521,549
Partner 5
403,454

28. Industry Experience: Chevron
Chevron installed eight VRUs at crude oil stock tanks in 1996

29. Industry Experience: Devon Energy
For 5 years Devon employed the Vapor Jet system and recovered more than 55 MMcf of gas from crude oil stock tanks
Prior to installing the system, tank vapor emissions were ~ 20 Mcfd
Installed a system with maximum capacity of 77 Mcfd anticipating production increases
Revenue was about $91,000 with capital cost of $25,000 and operating expenses less than $0.40/Mcf of gas recovered
This paid back investment in under 2 years

30. Lessons Learned
Vapor recovery can yield generous returns when there are market outlets for recovered gas
Recovered high Btu gas has extra value
VRU technology can be highly cost-effective in most general applications
Venturi jet models work well in certain niche applications, with reduced O&M costs.
Potential for reduced compliance costs can be considered when evaluating economics of VRU, EVRUTM or Vapor Jet

31. Lessons Learned (cont’d)
VRU should be sized for maximum volume expected from storage tanks (rule-of-thumb is to double daily average volume)
Rotary vane or screw type compressors recommended for VRUs where Venturi ejector jet designs are not applicable
EVRUTM recommended where there is gas compressor with excess capacity
Vapor Jet recommended where less than 75 Mcfd and discharge pressures below 40 psig

32. Discussion Questions To what extent are you implementing this BMP?
How can this BMP be improved upon or altered for use in your operation(s)?
What is stopping you from implementing this technology (technological, economic, lack of information, focus, manpower, etc.)?