Expander Operated Gas Processing April, 2015

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Gas Processing Expander

Colder Process Temperatures and Maximized Compressor Uptime with Helidynes Expander Skid.

Author:

Joseph James

Mechanical Engineer

April, 2015

Editor:

Andy Kerlin

Mechanical Engineer

Rev.3 Feb., 2016

Specifications:

Flowrates 1-10 mmscfd

Max. Pressure 1,440 psi

Min. Temperature -50 F

Power Generation up to 30 kW

Gas Processing Expander February, 2016

Table of Contents

Executive Summary 1

Introduction 2

J-T Skid Configuration 3

J-T/MRU Skid Configuration 4

Expander Skid Configuration 5

How It Works 6

Empirical Data & Validation 9

Mathematical Validation 11

Package Design 14

Contact Us 15

Gas Processing Expander February, 2016

pg. 1

Executive Summary:

Recent advancements in oil exploration and fracking in remote locations have significantly increased

production, particularly in North Dakota, where output has increased some 10 fold since 2003.

Unfortunately, development of pipeline infrastructure to transport the oil & gas product is either

economically infeasible or delayed many years to service these wells. Consequently, well owners must

rely on wellhead gas processing equipment as a means of separating the high value NGLs (Natural Gas

Liquids) from the flare gas in order to meet emission standards. And while transporting the NGLs by

truck is economical, capturing the remaining flare gas continues to be a challenge despite available CNG

and LNG post processing options. While some progress has been recently made, over 150 million cubic

feet of natural gas continues to be flared each day in remote areas of North Dakota.

Helidyne now offers well owners a new wellhead gas processing solution using its novel planetary rotor

expander. The expander increases NGL recovery rates, reduces flare gas and compressor downtime

while generating electricity as a byproduct.

Wellhead gas is traditionally refined by cooling processes which condense the heavier hydrocarbons

into their liquid state so the remaining lighter gas can be separated and flared. The most common

method of cooling is the J-T (Joule-Thomson) process. This approach requires a high pressure drop (500-

1,000 psi) across a J-T valve to achieve the desired downstream temperature. Depending on wellhead

gas composition, J-T skids have the capability of reaching temperatures ranging from -15 F to -35 F.

In contrast to the J-T throttling process, Helidyne uses the high pressure drop to drive its expander as

the primary means of extracting energy from the gas stream. Because this approach is much more

efficient, process temperatures will always be colder than a J-T under comparable conditions. This

results in more liquid recovery and higher revenue for the customer. On average, the Helidyne expander

will produce a 10-30 F colder exhaust temperature than a J-T valve. This document illustrates a few

configurations used within the industry, empirical data of the Helidyne expander, and how the Helidyne

expander skid is different.

Helidynes Model 4400 Expander

Figure 1

Gas Processing Expander February, 2016

pg. 2

Introduction:

Raw natural gas produced from a well is typically a byproduct of oil production and requires a certain

level of processing in order to meet flare emission regulations and/or pipeline specification. The

wellhead flowrate varies from well-to-well with the most common ranging between .5 - 3 mmscfd. This

raw gas contains many valuable components such as pentane (C5), isobutane (C4), and propane (C3)

which can be separated from the methane (C1) and sold to refineries as raw NGL mix for further

processing. Gas compositions with methane mol % ranging below 80% are considered rich wet gas

compared to 80% or above which are labeled dry or lean; wet gas being the more difficult to process.

Because many sites are remote, infrastructure (including

pipeline and electric grid power) is not available to

transport the raw gas. Shipping the gas in its unrefined

gaseous state via freight is not economical, as the

transport cost per cubic foot is unreasonable. For this

reason, wellhead gas processing equipment is used to

separate the NGLs from the methane so they can be

transported as a liquid to large refineries at a profit.

There are several approaches to condensing and dropping out the heavy hydrocarbons to make NGL.

The most common method is using an upstream heat exchanger coupled with a downstream J-T valve.

In this scenario, wellhead gas is compressed from 30-40 psi up to 1,000 psi with a temperature increase

to about 100-150 F. It then passes through the before mentioned heat exchanger that lowers the

temperature to 20-50 F, while maintaining the 1,000 psi pressure throughout this first stage (some of

the heavy gases liquefy at this stage and drop out). The now pre-cooled gas is then fed through a J-T

valve were a rapid drop in pressure utilizes the Joule-Thomson effect to lower its temperature further.

This J-T valve typically drops the pressure down to 100-300 psi and cools the gas in the range of -10 to -

30 F. Heavy gases liquefy, are extracted from the main gas stream, and then stored in large pressurized

tanks waiting for transport. The desired end products are high value NGLs and a gas with high methane

content (typically between 80% and 90% methane) which meets pipeline and flare requirements.

Occasionally, if wellhead gas is extremely rich

(40% - 60% methane), a MRU (Mechanical

Refrigeration Unit) is installed in-line with the J-T

valve to further cool the gas. Rich gasses

experience less temperature change when relying

solely on the J-T effect, so additional cooling from

a MRU is often needed to boost performance.

These refrigeration units demand large amounts

of electricity (approximately 125 kWe for

3mmscfd flow) that must be sourced from the

grid or an on-site generator, making this equipment addition an expensive proposition for the well

owner. Our experience has shown that MRUs operating on the rich gas in the Dakotas and western

Canada are often de-rated more than 50% and riddled with reliability problems that leave owners with

on-going repairs and downtime. The Helidyne expander skid is able to replace the J-T skid and MRU

altogether thanks to its ability to extract work-energy from the gas stream. The resulting temperatures

The Helidyne Expander

achieves colder

process temperatures

than the JT valve.

The Helidyne expander

will be a stand-alone, fully

automated mechanical

device that can be

remotely monitored.

Gas Processing Expander February, 2016

pg. 3

are between 10 and 30 F lower than a J-T valve, and comparable to a J-T+MRU combined process. But

unlike the MRU, the Helidyne expander generates power instead of consuming it; removing the need for

an on-site generator and the MRU itself.

Below are two common gas processing configurations. The first diagram (Figure 2) shows a J-T skid

configuration, which is typically used for leaner wellhead gas (80% methane content or higher). The

second diagram (Figure 3) shows the typical configuration for a wellhead with rich gas (Methane content

as low as 40%). Richer gases have steeper p vs. h charts (see fig.8 on page 7), which renders J-T

cooling less effective; thus requiring additional cooling from an electric powered refrigeration unit.

State Pressure Temperature Flow Description

1 30 to 40 psi 50 to70 F Rich wellhead gas (methane content between 40% and 80%)

2 1000 psi 100 to 150 F Hot, high pressure wellhead gas

3 1000 psi 30 to 60 F Cooled, high pressure wellhead gas/liquid mixture

4 150 psi 30 to 60 F Dropped out liquids collected from tank #1

5 1000 psi 30 to 60 F Cooled, high pressure wellhead gas (higher methane content then states 1-3)

6 150 psi -30 to 0 F Cold, low pressure gas/liquid mixture

7 150 psi -30 to 0 F Dropped out liquids collected from tank #2

8 150 psi -30 to 0 F Cold, low pressure gas (>80% methane content), used for heat exchanger

9 150 psi 30 to 70 F Cooled, low pressure lean gas sent for processing or flare

Reciprocating

Compressor

NGL

Collection

Tank

Separator

Tank #1

Separator

Tank #2

JT Throttling

Valve

Shell and Tube

Heat Exchanger

1

2

3

5

4

6

8

7

9

JT Skid Configuration (Typically used for leaner wellhead

gas applications, methane > 80%)

Figure 2

Gas Processing Expander February, 2016

pg. 4

JT/MRU Skid Configuration

(Typically used for rich wellhead

gas applications, methane < 70%)

State Pressure Temperature Flow Description

1 30 to 40 psi 50 to70 F Rich wellhead gas (methane content between 40% and 80%)

2 1000 psi 100 to 150 F Hot, high pressure we