Help - Gas Network Operator Handbook? 1

[Rgsherry]

Hi,

I am looking for a good handbook which details the responsibilities of a gas network operator ideally in different gas grid states.. For example, what are the degrees of freedom the operator has? If the pressure is too high in one part of the grid he may open another branch, use a storage area, control the compressor stations, or? I am quite new in this field so at this point any literature would be really great to have, because I have been looking for quite some time online and still haven't found anything on this topic. Many thanks in advance.

 

[Rgsherry]

This has proven to be a challenging task.. I can't seem to find any technical literature regarding the responsbilities and decision process taken by a gas network operator. Would anyone have any other recommendations? Should I try to get in contact with gas companies? I'm at a loss for ideas here. Hope someone can help..

 

[BigInch]

It's not all that complicated. They typically have interruptable customers and noninterruptable customers, or some variation thereof, as stated in their sales contracts. They must supply gas accordingly. Hospitals and other services will often have priority, as do residential customers. In times of short supply, some industries may have their supplies curtailed, or even cut off entirely. They have some sales volumes that are fixed, or slightly variable, and others that vary substantially, say with the weather. They also have purchase contracts, some fixed, some variable, some take or pay. Some contracts are long term, some short. They simply try to maximize profits, presumably sales, and minimize costs of purchased gas and costs of transmission, given the above contract restraints. They of course also have to deal with the physical restraints of their systems, such as delivery capacity at any point, gas in the system, supplies on line today, number of compressors running, demands near the sources verses demands near the end of the pipeline. To some extent they can use internal storage, or "line pack" to balance end of loads vs. beginning of pipeline loads. They can turn compressors on or off. They may be able to open other connections to emergency supplies, or parallel pipelines. They also may have storage tanks, caverns, old gas fields converted to storage, or an LNG ship on the way in. Take from one with the most, sell to the closest and highest priority, try to make a profit for their shareholders.
What else you need?

I hate Windowz 8!!!!

 

[austsa]

Network typically has 3 or more pressure regimes. Ideally, you'll route transmission pressure mains to extremities of the network. Then you'll have regulator stations (typically below ground) spread out to feed high/medium/low pressure to customers. HP and MP are regulated to LP prior to metering for domestic customers.
High downstream pressure should only occur if regulators fail open. OPSO valves (or relief valves) can be included at the design stage.

There are many issues to be considered in a network, including network modelling, need for dual-feed by two or more reg stations, increased risk of deliberate damage by public, unaccounted-for-gas, etc. There is a regular and frequent need to hot tap e.g. new service mains to new customers, etc.

For distribution pressures, there are more material options i.e. you don't have to use steel, with PE being very popular. Locating a PE pipe is not so easy, so there are issues to think about. Use of PE pipe allows squeeze-off, but risks need to be managed.

 

[Rgsherry]

Thanks BigInch, I appreciate the detailed response. I'm looking for any source material that I can academically reference, which has information similar to your response possibly with mathematical formulas used to assist network operators in making cost efficient/technically optimized decisions..

 

[BigInch]

Where I've seen these topics (excluding network analysis) discussed the most are in mathematical textbooks concerning the solution of optimization problems. Trouble is that only a few, if any, are taken from gas networks.

I hate Windowz 8!!!!

 

[Rgsherry]

Thanks for the reply Austsa. Just to clarify, I am only researching the transmission of natural gas at high pressures. I was thinking about trying to dig up some journals or possibly contacting companies directly for this type of information. Any recommendations would be greatly appreciated.

 

[Rgsherry]

Here are some of the basic questions I'm still searching to understand both conceptually and mathematically:

1. What can you do to control/vary the pressure level and mass flow? Which tools can you use, without influencing the customers?
2. What happens to the pressure level/mass flow when you connect an additional pipeline at the connection point? How is the storage volume of the network affected?
3. What happens to the pressure, storage volume, and mass flow when you are switching off a pipeline?
4. What happens with the mass flow/pressure if you have an additional feed-in/feed-out?
5. What happens if you use valves to reduce/increase a mass flow in one pipeline of the network?
6. How can you describe these relations mathematically?
7. What is the relation between pressure level and stored volume in the network?

I hope somebody can help. Thank you in advance.

 

[austsa]

For a metropolitan gas network, network computer modelling does most of your questions. There are software you can purchase to do this modelling. Google gas network modelling software.
A planning dept would do this modelling work, designing the reticulation, with some spare capacity. They'll advise the engineering dept where they need regulator stations and what inlet pressure is available, what outlet pressure is required and max/min flows are expected.
Mostly, when an additional customer is connected, this isn't a problem as domestic consumers doesn't consume much gas. For new industrial customer, a suitable feed main is selected. This is not always the closest main to the site, due to capacity, pressure, etc of the closest main.
Over time, a trunk main may approach its capacity, and a decision is required whether to add a duplicate main, or replace the existing main with a larger diameter.
So, my answers to your questions:
1. Network modelling determines the network pressures. Pressures are achieved by regulator stations distributed within the network.
2. If the main has spare capacity, then the pressure doesn't fall. Note, that even without new customers, customer demand isn't constant all year round. Typically, much higher usage in winter vs summer, for example. So, the network must be designed to handle this.
3. Switching a pipeline off is something that I've come across. Do you mean decommission? What are the reasons you would want to switch off a main?
4. See 2.
5. Network control by throttling valves is something you would want to avoid. You could accidentally starve a main of gas, air would get in, and it is a big job to revive the main.
6. Computational fluid dynamics
7. The larger the volume:
- the less pressure variation you'll have when a small amount of gas is consumed
- regulator stations will not have to work as hard

 

[austsa]

3 should read
Switching a pipeline of is something that I haven't come across.

 

[Rgsherry]

Okay so it seems by the responses I've received, that a gas network operator isn't typically directly involved with considering the physical constraints of the system. But they are responsible for controlling the flow of the gas correct? To control this gas flow you must know proper/safe pressure values to get it form point A to point B via however many pipelines/valves must be used - and so this information (the proper pressure and mass flow values) are supplied to the network operator by the planning department?

For example, the network operator will make a decision when to store gas in a storage site or when as line pack correct? How does he make these decisions on a technical level? For instance, when filling a gas storage site, how does he know how much to store and at what pressures/mass flows etc? Is this all automated for him so he doesn't have to really think about it?

Sorry if my questions seem very fundamental, but this is all very new to me. I appreciate the responses you've all given. I'm still trying to get a firm grasp on these concepts.

 

[LittleInch]

It all depends on whether the gas transport operator is moving his own gas or simply acting as a transporter of other peoples gas.

The UK gas network is a transportation system and many similar systems in Europe are gradually going the same way supposedly to enhance competition between suppliers or "shippers". Hence the commercial decision about when to store gas or take it from LNG facilities or source from one particular input point rather than another is a commercial one undertaken by the shippers. The transporter has a duty then to make it all work and has entire departments constantly looking at how to this in the most efficient manner by means of a constant running network model updated with real numbers. The transporter makes money by transporting gas in the most efficient manner possible and the shipper by selling it at the best price he can and sourcing it a the lowest price he can.

Over time the gas system operators gain an understanding of "typical" flows and the impact of different predicted temperatures on gas supplies and plan accordingly. All the shippers are required to balance their outflow to customers with inlet volumes to match. If they don't then the system might fail, but in reality the transporter has powers to buy gas needed to balance the network and then back charge the shippers along with a fine for not balancing his flows. The operation of this is a regulated function governed by a set of rules about 100 pages long called the "Uniform Network Code". See this

http://www.gasgovernance.co.uk/unc

for further details.

I think you really need to try and talk to the planning department of a large scale operator if you want to discover more, but I wish you luck in this as often this is seen as confidential information.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Rgsherry]

Thank you, I downloaded the UNC from the link you posted.. I'm not sure how much info there will help me, but I will look through it closely. I was afraid what you said may be true. This information I'm seeking does seem to border on the line of confidentiality, but I'm still in disbelief that there is no literature covering some of these practical and fundamental questions. I've been searching endlessly through countless numbers of databases and university libraries for my useful information. I don't know if I'm just looking in the wrong places, searching for the wrong terms, or if these details are just not made available to the public. In my case it's not a choice because unfortunately this is the thesis topic I chose and I have to not only find this information, but use C++ to simulate it after. It's not looking too good at the moment. Anyway, I hope someone else has some advice. This has been the most feedback I've gotten so far throughout the last two months.

 

[LittleInch]

The thing is that this sort of thing is only really of interest to gas transmission system operators and due to the wide differences in systems what works or is applicable in one country doesn't work in another. For instance gas storage Germany is up to 35 - 40% of the annual gas demand, but only 5% or less in the UK which makes usage of storage systems completely different. Ditto use of gas for electrical power generation or not. The only constant in gas network planning is change (of demand profile, usage, inlet points, storage usage etc)

Many transmission systems are effective monopolies, often nationalised or government institutions (or were) and the first thought of most of them is to say nothing or restrict access to information on the basis of national security or commercial confidentiality.

Your best bet IMO is to try and talk to a sympathetic gas network planner in an transmission company and get your information from them.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way