Module 5 - Field handling of Natural Gas

Question 1

When are gas hydrates formed?

Answer 1

When high concentrations of water and methane under certain conditions of temperature and pressure combine together to form a solid. This formation leads to solid hydrates forming which grow and eventually completely plug off the flow

Question 2

What is the best way to handle gas hydrates?

Answer 2

Proactively try to prevent them form forming in the first place.

Question 3

The dew point, at a given pressure, is the temperature at which what happens?

Answer 3

The first drop of liquid is observed.

Question 4

What is the most common method of observing a dew point?

Answer 4

Capture a sample of natural as and then while constantly monitoring the temperature, cool the sample in a chamber until the first drop of liquid is visible.

Question 5

At the dew point, is the gas sample unsaturated or saturated with water? So therefore the dew point is a measure of..?

Answer 5

Saturated. A measure of the amount of seater in the gas.

Question 6

What is used extensively to determine the water content in the gas from an observed drew point temperature?

Answer 6

The GPSA Engineering Data Book

Question 7

What does GPSA stand for?

Answer 7

Gas Processors Suppliers Association

Question 8

The GPSA Chart can also show what?

Answer 8

Shows the drew pint where hydrate formation will occur at a given temperature and pressure.

Question 9

Describe what a line heater is and the purpose of it

Answer 9

They are a shell and tube heat exchangers that heat natural gas and liquids flowing in a pipeline indirectly through a heat medium such as ethylene glycol.

Question 10

What is the main purpose of a line heater?

Answer 10

Raise the temperature of a the fluids flowing in the pipeline above the hydrate formation temperature.

Question 11

What is the process for gas to be heated with a liner heater?

Answer 11

1) Gas heated by passing through a pre-heat coil in the heat medium (above the temp where hydrates form)
2) Gas directed through the throttle valve to drop the pressure as required by the pipeline or process
3) Passes through the heat medium again via a heat-coil to ensure the exit temperature of the gas is high enough for the gas to arrive at tits destination above the min hydrate temp

Question 12

Line Heater requirements are based on what unit per what unit

Answer 12

BTU’s per hour

Question 13

What is the normal standard incremental BTU/hour in Alberta for line heaters?

Answer 13

Build them in 250,000 BTU per hour increments.

Question 14

Are line heaters expensive? and if so, what may be used to replace them?

Answer 14

Line heaters are very expensive, and cause extra complication when considering the installation and operation of the gas facility.
The use of Hydrate Inhibitors

Question 15

What are the common Hydrate Inhibitors?

Answer 15

Chemicals such as Methanol or Glycol

Question 16

How do hydrate inhibitors work?

Answer 16

By dissolving water, this changing its chemical properties so that it cannot form the lattice structure and trap natural gas.

Question 17

To be effective, a hydrate inhibitor must be present when?

Answer 17

When the wet gas is cooled to its hydrate temperature

Question 18

When is methanol commonly injected and why?

Answer 18

Injected just before valves that cause enough pressure drop to oil the gas into the hydrate formation envelope.

Question 19

What equation is used to approximate the amount of methanol needed to be injected?

Answer 19

Hammerschmidt’s 1934 equation

Question 20

The amount of inhibitor required must also take into account for what fact?

Answer 20

That the inhibitors are volatile and will vaporize.