9 replies to this topic

[patrickk]

I'm facing some trouble with a design problem. I am trying to design an lng processing plant and am having trouble finding information on how to power the plant as electricity in the area is very expensive due to the plants remote location. I am planning to primarily use ethane and propane recovered from the natural gas as a fuel. I have no problems extracting the ethane and propane however i am not sure of the exact steps I will need to use this in order to fuel the plant. If someone could point me in the right direction it would be greatly appreciated! thanks!

[ankur2061]

patrick,

If you have sufficient gas available you can generate your own electricity (captive power plant) using Gas Turbines connected to a generator:

Have a look at the wikipedia article on gas turbines at the link below:

http://en.wikipedia....ower_generation

Another link outlines the basic principle of electricity generation using various means:

http://www.electrici...generation.html

This should give you a`start on using lean gas (predominantly methane) for gas turbines.

Additionally, if you can lay your hands on GPSA Engineering Databook, 11th edition, Section 15, "Prime Movers" a whole sub-section is dedicated to gas turbines which should provide you good guidance.

Your gas turbine system should be the first one built before the other units/plants receiving power from your captive power plant. Power during construction, commisioning & start-up operations may be derived from temporary sources such as large stand-alone diesel generators or engines which are readily available.

Hope this helps.

Regards,
Ankur.

Regards,
Ankur.

[Art Montemayor]

Patrick:

I think you are going about your solution in the wrong way.

Hydrocarbons are generally priced in one of two ways: fuel value and comodity value (market value). I believe you will find that propane and ethane are priced on availability and as a comodity first, since they tend to be more scarce. Natural gas should be cheaper or less expensive as a fuel (it is more readily available).

I would follow Ankur's advice and base electrical generation on natural gas firing.

[Zauberberg]

Whichever of the commercial LNG technologies is selected for your plant (e.g. like CoP or APCI), there will be plenty of fuel gas from the Liquefaction train to meet your energy demands. Particularly if the feed gas contains Nitrogen in significant proportions, you want to utilize Methane compressor discharge stream as a high-pressure fuel gas for turbine, or Nitrogen Rejection Unit flash vapor in case of APCI process.

As Art has pointed out, using C3+ as fuel gas is quite a luxury - you should be recovering these as liquid products and increase your profit margin. Very common configuration in remote locations is to utilize GTG's (Gas Turbine Generators) for producing power, and the most lean gas should be used for that purpose. Feed gas will be used for startup purposes only.

Here's a link to the GE website where you can ask for budgetary quotation: http://www.gepower.c...avy_duty_gt.htm or contact Siemens to see if any of their models fits your needs: http://www.energy.si...chuere_E_LR.pdf

Best regards,

[patrickk]

Thanks for the advice everyone. Ok so I shall sell the hydrocarbons as a by-product of my process. I will use some of the natural gas as a fuel source to run my process. Zauberberg you mentioned that nitrogen in the feed gas will have an effect upon the energy generation, my feed gas has a nitrogen content of 0.75mol%, will this be an issue?

Assmuing this will not be an issue, I shall burn some of the feed natural gas (consisting of approx 80%CH4, 13%ethane, 4%propane, 3%CO2, and small amounts of elements such as nhydrogen nitrogen etc.) in my turbine which I shall then have connected to a generator. Does anyone know of any lng process plants currently using this technique so i could have a look at the pfd and design details on the net?

Thanks for the help.

[Zauberberg]

Discharge as much Nitrogen as you can from the Feed gas to the Fuel gas system. As said, the CoP Cascade process does this in the open Methane compressor loop, the APCI process does the same through LNG flash drum and Nitrogen Rejection Unit. No concerns regarding the N2 content in turbine fuel gas.

Feed gas is normaly used as the turbine fuel gas only during startup, i.e. when process discharge streams are not available yet. Depending on how much power you need for the plant + surroundings, you may have to burn additional quantities of Feed gas - but remember not to burn C3+ as these are the money makers.

The design information you are looking for is proprietary and as such not available on the internet. Some general information about the CoP Cascade process and the APX process from Air Products can be found on their websites.

Best regards,

[djack77494]

I shall burn some of the feed natural gas (consisting of approx 80%CH4, 13%ethane, 4%propane, 3%CO2, and small amounts of elements such as nhydrogen nitrogen etc.) in my turbine which I shall then have connected to a generator.

patrickk,
I would be a bit concerned over the large concentrations of heavier (than methane) hydrocarbons. I don't know what your process conditions are, but you may be in danger of generating some condensate, especially if you might start with moderate (ambient) temperatures and high pressure. Remember you will get temperature drops where you drop pressure. Key to successful operation of a gas turbine is keeping liquids out of the fuel supply. Besides disrupting the combustion process, they will wreck havoc with your environmental performance.

[patrickk]

ok for the bulk of the electricity generation i will be using natural gas removed just prior to the liquefaction process. for a 8.2megatonnes of lng per annum producing plant which turbine and generator would u recommend? and for calculating the energy produced is it a simple process of using the element compositions and finding out the energy given off when combusted and multiplying that by the turbine and generator efficiencies?
cheers

[Zauberberg]

That is a huge plant (8.2 MMTPA). If you are speaking about single processing train, then it looks like the Frame 9E model is definitely your choice.

As far as energy is concerned, you will obtain the familly of curves (Power Output and Heat Rate) from the vendor, for range of ambient temperatures, humidities, etc.

See some interesting info at:

http://www.gepower.c...ct225_lorez.pdf
http://www.airproduc..._Is_Greener.pdf
http://www.airproduc...PS26Roberts.pdf
http://lnglicensing....nts/scaleup.pdf

[Zauberberg]

Also see attached file:

Attached Files

•  Driver Selection For LNG Plant Compressors.pdf   2.77MB   26 downloads