# Presentation: 579245

## Installing Vapor Recovery Units to Reduce Methane Losses

**Lessons Learned from Natural Gas STAR**
**Producers Technology Transfer Workshop**
**Devon Energy Corporation**
**and**
**EPA’s Natural Gas STAR Program**
**April 20, 2005**

## Vapor Recovery Units: Agenda

- Methane Losses
- Methane Savings
- Is Recovery Profitable?
- Industry Experience
- Discussion Questions

## Methane Losses from Storage Tanks

- Storage tanks are responsible for 15% of methane emissions
**96% of tank losses occur from tanks without vapor recovery**

- Inventory of U.S. Greenhouse Gas Emissions and  Sinks 1990 - 2002

**Pneumatic Devices**
**60 Bcf**

**Meters and**
**Pipeline Leaks**
**11 Bcf**

**Gas Engine Exhaust**
**12 Bcf**

**Well Venting **
**and Flaring**
**12 Bcf**

**Storage Tank **
**Venting**
**23 Bcf**

**Other Sources **
**15 Bcf**

**Reciprocating **
**Compressors**
**3 Bcf**

**Dehydrators **
**and Pumps**
**14 Bcf**

**Notes:**
The numbers here are from the 2002 inventory.

.425 Bcf from tanks with control devices / (2.26 + 7.877 Bcf)   = 4% of tank emissions are from tanks with control devices  (this is from 2003 petroleum and gas inventories)

## Sources of Methane Losses

- 23 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

- * Inventory of U.S. Greenhouse Gas Emissions and  Sinks 1990 - 2002

**Notes:**
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
THESE NUMBERS WERE REPLACED WITH THE PREVIOUS YEAR’S NUMBER OF 23 BCF TO MATCH THE PIE CHART (23 BCF includes natural gas STAR reductions)

## 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**

**Notes:**
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.

## 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 (EVRUsTM)
**Use Venturi jet ejector in place of rotary compressor**
**Do not contain any moving parts**
**Require source of high pressure gas and intermediate pressure system**

## Standard Vapor Recovery Unit

**Control**
**Pilot**

**Vent Line**
**Back Pressure**
**Valve**

**Suction**
**Line**

**Condensate **
**Return**

**Bypass**
**Valve**

**Electric**
**Control**
**Panel**

**Electric Driven**
**Rotary Compressor**

**Gas Sales**
**Meter Run**

**Gas**

**Liquid **
**Transfer Pump**

**Check Valve**

- Source: Evans & Nelson (1968)

**Sales**

**Notes:**
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.

## Venturi Jet Ejector*

**High-Pressure**
**Motive Gas**
**(~850 psig)**

**Flow Safety Valve **

**Pressure Indicator**

**Temp Indicator**

- PI

- TI

- TI

- PI

**(-0.05 to 0 psig)**

**Low-Pressure Vent Gas from Tanks**
**(0.10 to 0.30 psig)**

- PI

- TI

**Discharge **
**Gas **
**(~40 psia)**

**EVRU****TM**** Suction Pressure**

- *Patented by COMM Engineering

**Notes:**
The pressure readings shown are for a specific example.

## Vapor Recovery with Ejector

**Vapor Recovery with Ejector**

- Oil to Sales

- Gas to Sales
- @ 1000 psig

- LP Separator

- Oil

- Gas

- Compressor

- Ejector

- Oil & Gas Well

**5,000 Mcf/d Gas**
- 5,000 Bbl/d Oil

**900 Mcf/d**

- Ratio Motive / Vent = 3
-                      = 900/300

**300 Mcf/d Gas**

- 40 psig

- 6,200 Mcf/d

- Crude Oil Stock Tank

**(19 Mcf/d Incr.fuel)**

**281 Mcf/d**
**Net Recovery**

## Example Facility for EVRUTM

- Oil production:		5,000 Bbl/d, 30 Deg API
- Gas production:		5,000 Mcf/d, 1060 Btu/cf
- Separator:			50 psig, 100oF
- Storage tanks: 		4 - 1500 Bbls @1.5oz relief
- Gas compressor:		Wauk7042GSI/3stgAriel
- Suction pressure:		40 psig
- Discharge pressure:	1000 psig
- Measured tank vent:	300 Mcf/d @ 1,850 Btu/cf

## Emissions Before EVRUTMCO2 Equivalents

- Engine exhaust:   	3,950 Tons/yr @ 790 Hp load
- Tank vents:         		14,543 Tons/yr
- Total CO2 equivalents:	18,493 Tons/yr
- Fuel consumption @ 9000 Btu/Hp-hr = 171 MMBtu/d
- Gas sales:			5,129MMBtu/d
- Gas value:	   		$25,645/d @ $5/MMBtu

## Emissions After EVRUTMCO2 Equivalents

- Motive gas required:			900 Mcf/d
- Engine exhaust:			4,897 Tons/yr @ 980 Hp load
- Tank vents:				0 Tons/yr
- Fuel consumption @ 9000Btu/Hp-hr:	190 MMBtu/d
- Total CO2 equivalents:			4,897 Tons/yr
- Reduction:				13,596 Tons/yr (73.5%)
- Total CO2 equivalents:			4,897 Tons/yr
- Reduction:				13,596 Tons/yr (73.5%)
- Gas sales:				5,643 MMBtu/d
- Gas value:				$28,215/d @ $5/MMBtu
- Income increase:			$2,570/d = $77,100/mo
**EVRU cost installed:****	****	****	****$75,000**
- Installed cost per recovered unit of gas: 	$0.73/Mcf/yr
**Payout:****	****	****	****	****<1 month**

## Vapor Recovery Unit Decision Process

**IDENTIFY possible locations for VRUs**

**QUANTIFY the volume of losses**

**DETERMINE the value of recoverable losses**

**DETERMINE the cost of a VRU project**

**EVALUATE VRU project economics**

## Criteria for Vapor Recovery Unit Locations

- Steady source and sufficient quantity of losses
**Crude oil stock tank**
**Flash tank, heater/treater, water skimmer vents**
**Leaking valve in blanket gas system**
- Outlet for recovered gas
**Access to gas pipeline or on-site fuel use**
- Tank batteries not subject to air regulations

**Notes:**
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.

## 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 ultrasonic meter (± 5%)
- Measure losses using recording manometer and orifice well tester (± 100%)

**Notes:**
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.

## Estimated Volume of Tank Vapors

- Pressure of Vessel Dumping to Tank  (Psig)

- Vapor Vented from Tanks- cf/Bbl - GOR

- 110

- 100

- 90

- 80

- 70

- 60

- 50

- 40

- 30

- 10

- 20

- 10

- 20

- 30

- 40

- 50

- 60

- 70

- 80

- Under 30° API

- 30° API to 39° API

- 40° API and Over

## Quantify Volume of Losses

- E&P Tank Model
**Computer software developed by API and GRI**
**Estimates flash, working and standing losses**
**Calculates losses using specific operating conditions for each tank**
**Provides composition of hydrocarbon losses**

**Notes:**
The model is an accurate, user-friendly method to estimate gas (light hydrocarbon) losses from an oil stream during the production process.  The model allows the operator to enter specific operating conditions for each tank, which provides greater accuracy.  

The E&P Tank model also generates data on the composition of the vapors emitted – something neither other method does.  This is critical because it enables the user to determine more accurately the value of the lost gas.  It can also distinguish between HAPs and volatile organic compounds (VOCs), which is significant for air quality monitoring.

## 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**

**Notes:**
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.

## 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

**Notes:**
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. 

## Cost of a VRU

- Major cost items:
**Capital equipment costs**
**Installation costs**
**Operating costs**

## Value of NGLs

## Cost of a VRU (cont’d)

## Is Recovery Profitable?

## Trade Offs

|  | Conventional VRU | Ejector |
| --- | --- | --- |
| Fuel for electricity (Mcf/yr) | 2,281 | _ |
| Fuel (Mcf/yr) | _ | 6,935 |
| Operating factor | 70% | 100% |
| Maintenance | High | Low |
| Installed cost per recovered unit of gas ($/Mcf/yr) |  $1.21 | $0.73 |
| Payback (excl. maintenance) | 3 to 27 months | <1 month |

**Notes:**
Conventional VRU installed cost per Mcf/yr:   $77,000 /[ 250 Mcfd * 365 * 70%]
eVRU: $75000 /[ 281 Mcfd * 365]

## Mechanical VRU advantages
Gas recovery
Readily available

Mechanical VRU disadvantages
Maintenance costs
Operation costs
Lube oil contamination
~ 70% runtime
Sizing/turndown 

- Mechanical VRU advantages
**Gas recovery**
**Readily available**
- Mechanical VRU disadvantages
**Maintenance costs**
**Operation costs**
**Lube oil contamination**
**~ 70% runtime**
**Sizing/turndown**** **

- EVRU advantages
**Gas recovery**
**Readily available**
**Simple technology**
**100% runtime**
**Low O&M costs**
**Sizing/turndown (100%)**
**Minimal space required**
- EVRU disadvantages
**Need HP Motive Gas**
**Recompression of motive gas**

## Lessons Learned

- Vapor recovery can yield generous returns when there are market outlets for recovered gas
**Recovered high Btu gas or liquids have extra value**
**VRU technology can be highly cost-effective**
**EVRU****TM**** technology has extra O&M savings, higher operating factor**
- Potential for reduced compliance costs can be considered when evaluating economics of VRU/EVRUTM

## 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 there is no source of high-pressure gas and/or no intermediate pressure system
- EVRUsTM recommended where there is gas compressor with excess capacity

## 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  |

## Industry Experience: Chevron

- Chevron installed eight VRUs at crude oil stock tanks in 1996

## Vapor Recovery Units

- Profitable technology to reduce gas losses
- Can help reduce regulatory requirements and costs
- Additional value of NGLs further improves cost-effectiveness
- Exemplifies profitable conservation

## 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.)?