CO2 Engineering Portal: Oil and Gas
Showing posts with label Oil and Gas. Show all posts
Showing posts with label Oil and Gas. Show all posts

Sunday, 12 February 2012

Use Wobbe Index to Manage Fuel Quality to Gas Burner


Gas turbine generator or gas turbine driven compressor is common used in refinery, LNG and gas plant. These turbine basically will burn gas fuel from the plant itself and hot flue gas is passed through the gas turbine. Gas turbine is then rotate and drive motor or compressor to generate power and head.

Gas fuel burnt in gas burner which typically has fixed orifice nozzles. Heat output from the fixed orifice burner is proportional to flow (Q) and heating value (HV) of the gas fuel. As fuel composition change, flow and heating value will have to be changed to maintain a correct heat output. However, the magnitud of flow and heating value changes may not change linearly or there is not fix relation between flow and heating value. How to relate these two parameters ?

Continuous Changes in Fuel Heating Value (HV)
Gas fuel from refinery, LNG or gas plant is normally a mixtures of gas from several sources i.e. waste gas with low, medium and high heating value. A typical example is fuel gas system in LNG plant. Fuel source can be 

  • End Flash Gas which contains very high inerts (as high as 50%-55% Nitrogen level) and low heating value
  • Flash gas from Amine regeneration unit which contains high level of CO2 and H2S, Hydrocarbon component varies from ethane to Decane including BTEX
  • Demethaniser overhead which contain high Methane level
  • Boil-off gas (BOD) which contains very high level of methane and low level of nitrogen
  • Flash gas from Ethane, Propone, and LPG storage
  • Make-up which composition varies from Methane to Decane

These gases will have large differences in composition, high heating value(HHV), low heating value(LHV) , specific gravity (SG), etc. As the flow for each sources may change due to dynamic of the plant and above value will change dynamically from time to time. How to manage the dynamic changes ?


How to manage a the flow and heating value which may vary in different magnitude and continuous variation in source heating value whilst maintaining a constant heat input into the gas turbine ? What are the parameter to be maintained or limited ?

Wobbe Index is the parameter. Mr. Wobbe found that
  • Flow is proportion to gas specific gravity (SG) and;
  • Heating Value is also proportion to gas specific gravity (SG)
Wobbe Index (WI) is define as

WI = HHV / Sqrt (SG)
where
Sqrt = Square root of
HHV = High Heating Value (Btu/Scf)*
SG = Specific Gravity (MWgas / 28.96)

* Some may use Lower Heating Value to define WI

This is the parameter that gives a relative measure of the mix/heating value. 
Wobbe Index is used to compare the combustion energy output of different composition fuel gases. Two fuels with identical Wobbe Index at given pressure and valve setting (orifice size) the energy output will be identical. The variation in WI is typically upto 5% (but maximum could be 10% for some manufacturer).

Thus, plant fuel gas designer shall design the fuel gas system such that the fuel gas mixture feeding into the gas turbine meeting the WI limitation. In the event of any upset or interference of any fuel supply source, the control system shall be able to maintain the WI within the limitation.
Calculations of Specific Gravity, Calorific Value & Wobbe Index Table Excerpted From The Institute of Gas Technology, bulletin No. 32
  • Wobbe Index is a measure of the amount of energy delivered to a burner via an injector (orifice). The energy input is a linear function of Wobbe index.
  • Two gases differing in composition but having the same Wobbe Index will deliver the same amount of energy for any given injector/orifice under the same injector pressure. 
  • In natural gas appliances, the gas flow is restricted by passing it through an orifice (hole). The Wobbe Index is useful because for any fixed orifice size and gas pressure, any gas compositions that have the same Wobbe number will deliver the same amount of heat energy or expressed as interchangeability of varying gas compositions.

Interchangeability; Wobbe Index

According to ISO-13686, gas interchangeability indicates the degree of substitutability between the combustion characteristics of different gas types.
Gas with one particular composition is interchangeable with another having a different composition, only if the quality of combustion remains within the specified range.
The Mexican NOM uses the Wobbe Index to deal with gas interchangeability. This index shows the relationship between heat value and the specific gravity of gas, as a flow of energy at constant pressure.
Gas with different compositions but the same Wobbe Index provides the same amount of energy at the same pressure (Fig. 3).
This relationship is represented by a flow equation at the flow point, as follows: W=HHV/ (squareroot of)sg ; where W= Wobbe Index; HHV=high heat value; and sg=specific gravity.

Sources: 



    Sunday, 16 October 2011

    Top 10 Gulf Mega Projects


    Client: Dow Chemical/Saudi Aramco
    Scope: Over 11 million tpa of various petrochemical and chemical products.  
    Status: Due for completion in 2015.
    Estimated Cost: US$27 billion
    Known Contractors: KBR have been awarded the project management contract. Remaining contracts out to tender in 2010.

    When the world’s largest oil company joins forces with the world’s largest chemical company you know that the end result is going to be big . And RITP is very very big.

    The facility will be the largest facility of its kind in the world and will produce a huge range of products including ethylene, propylene, aromatic, chlorine derivatives, polyethylene, ethylene oxide and glycol. It will also be connected to the Ras Tanura Refinery complex and its Jua’ymah gas processing plant.

    The project further underlines Saudi Arabia’s massive expansion plans in regards to the petrochemicals industry. Output from the plant will be aimed at the export market 
    The completion date has come under scrutiny recently with reports that the project could be delayed for one year.
    2.                  Pearl GTL (Qatar)

    Client: Qatar Petroleum
    Scope: 140,000 bpd clean-burning fuel and other products, 120,000 barrels of oil equivalent per day of natural gas liquids and ethane.
    Status: Due for completion in 2010.
    Estimated Cost: $24 billion (up from an original estimate of $5 billion)
    Known Contractors: JGC Corporation, Kellogg Brown and Root, Halliburton, MW Kellogg Ltd, Honeywell, Shell, General Electric.

    Pearl GTL will be the world’s largest plant converting natural gas into clean-burning liquid transport fuel and other products. The construction of Pearl is ongoing at Ras Laffan on Qatar’s coast. More than 40,000 workers currently work onsite, making it one of the world’s largest industrial developments.

    Of the two million tonnes of prefabricated parts for the GTL plant and equipment, including 12,200 kilometres of cables, about half has already arrived.

    A gigantic crane is currently lowering steel GTL reactors - at 1,200 tonnes each is as heavy as seven jumbo jets - on to concrete bases in the heart of the plant. Twelve of the 24 cylinder-shaped reactors central to making GTL products have been installed so far. Some are built in Germany. Barges ferry the giant reactors, each containing hundreds of kilometres of pipes along the Rhine to the Dutch port of Rotterdam. From there, they are shipped to Qatar.

    Drilling is under way. Sixty kilometres offshore, preparations to produce the raw gas from the North Field are well under way. Two platforms sitting in water up to 40 metres deep will feed gas to the plant. The steel structures, or jackets, to support the platform are already in place on the seabed.

    3.                   Petro Rabigh Refinery Upgrade (Saudi Arabia) 

    Client: Saudi Aramco/Sumitomo
    Scope: 2.4 million of petrochemical solids and liquids plus large volumes of gasoline and other refined products.
    Status:  Commissioning started in March
    Estimated Cost: $10 billion
    Known Contractors: Shaw Stone & Webster, JGC, Maire Tecnimont, Mitsui Engineering & Shipbuilding, Shell, Foster Wheeler, Invensys Process Systems.

    Petro Rabigh is another huge Saudi project and the finished result will be one of the world’s largest integrated oil refining and petrochemical facilities.
    The joint venture between Saudi Aramco and Sumitomo Chemical Co of Japan will refine Arabian Light crude oil to produce high-value light petroleum products. The complex will also produce ethylene, propylene and other refined products. 

    Sumitomo Chemical and Saudi Aramco each hold a 37.5% stake in Petro Rabigh, while the remaining 25% is owned by public investors, following an IPO which took place in early 2008.

    4.                   Shah Sour Gas Field Development (UAE)

    Client: Abu Dhabi National Oil Co (ADNOC)
    Scope: Production and processing facilities for extremely sour gas field.
    Status: Flour Corp. finished the initial engineering and design work on the Shah Gas Development last month and 10 contract packages are now being prepared for tender to be awarded “within the year”,
    Estimated Cost: $10 billion
    Known Contractors:
    ConocoPhillips
    Desalination, construction and industrial power demands are increasing at an exponential rate, and though efforts such as the Masdar initiative will curb future requirement growth, it is essential the UAE works to harness the assets at its disposal.
    The dolphin project is now running at full consumption of its current phase and the gas that's supplied to the UAE is very close to maximum capacity, so alternatives need to be looked at.

    In the short term it's imperative that the UAE exploits what resources it possesses , and there are considerable sour gas reserves,"" explains Nick Coles, founder and organiser of the SOGAT conference and exhibition.

    The UAE's estimated natural gas reserves stand at around 214 trillion cubic feet. This puts the UAE fourth among the largest natural gas reserves in the Middle East after Iran, Qatar, and Saudi Arabia.

    However, the high sulphur content of that gas has made full exploitation problematic up to now. Abu Dhabi holds the dominant share of the country's reserves with proven fields of around 195 trillion cubic feet.

    In Abu Dhabi the complexities envisaged in the development of the Shah and Bab fields have led to a rethink as to how best to optimise the gas potential of these sour fields against the considerable financial requirements involved, with the sour gas development project initiating these significant developments.

    ADNOC have put out a tender to develop the Shah and Bab fields in conjunction with an IOC. This will expedite field development in the short term, and concurrently provide gas to fuel the UAE's considerable industrial, commercial and domestic power requirements," says Coles.

    5.                  Khurais Oilfield (Saudi Arabia)

    Client: Saudi Aramco
    Scope: 1.2 million bpd oil, 315 million scfd sour gas, 70,000 bpd natural gas liquids 
    Status: Almost completed, due to start production June 2009
    Estimated Cost: $10 billion
    Known Contractors:  SNC-Lavalin, Saipem,  Halliburton, Jacobs Engineering, SNC Lavalin, Saudi Consulting Services, Foster Wheeler Energy Limited

    To put Saudi Aramco’s $10 billion Khurais oilfield project into perspective, the three fields involved in this huge venture, Khurais, Abu Jifan and Mazalij, hold 27 billion barrels of oil. This is more oil than the all of the proved reserves of the United States.

    Khurais is the key component of Saudi Arabia’s bid to boost oil production by an extra 2 million bpd and nothing has been left to chance. The project involves the construction of a central processing facility, providing crude processing and stabilisation facilities, new wells and trunklines, a saltwater injection system, as well as a large residential and industrial complex.

    With a completion date set for June 2009 the Khurais project has been some 46 years in the making. Situated close to Ghawar, the world’s largest oilfield, Khurais will provide an additional 1.2 million barrels per day Arab light crude to the KSA’s production capacity.

    The project will also produce 315 million scfd of sour gas for the Shedgum Gas Plant and 70,000 bpd of natural gas liquids (NGL) for the Yanbu Gas Plant.

    6.                  Manifa Offshore Oilfield (Saudi Arabia) 

    Client: Saudi Aramco
    Scope: 900,000 bpd oil, 120 million scfd sour gas, 50,000 bpd condensate, 950,000 bpd of produced water
    Status: Due to start production mid-2011
    Estimated Cost: $9 billion
    Known Contractors:
    Saipem, Halliburton, Foster Wheeler, Tecnicas Reunidas, Jan De Nul Group

    The $11 billion Manifa (also known as Moneefa) project will be Saudi Aramco’s largest offshore field when fully operation and will add 900,000 bpd of extra capacity to Saudi Arabia’s oil output.
    As well as the heavy crude, the Manifa field will also produce 120 million scfd of sour gas, 50,000 bpd of condensate, and 950,000 bpd of produced water.

    The huge outlay is being spent on constructing a number of drilling islands, a central processing facility, a water injection system, downstream pipelines,  and a massive 41km causeway that runs to shallow-water offshore platforms. This will facilitate the easy transportation of goods and services both to and from the mainland. The nearby Khursaniyah Gas Plant is also being upgraded to cope with the additional gas from the project.

    7.                  Saudi Kayan Petrochemicals Complex (Saudi Arabia)

    Client: SABIC/Kayan Petrochemicals
    Scope: Six million tpa of petrochemical and chemical products
    Status: Expected to go onstream late 2010
    Estimated Cost: $9 billion
    Known Contractors:
    Kellogg Brown and Root, Fluor, Samsung Engineering, Simon Carves, Tecnicas Reunidas, Van Leeuwen Pipe and Tube,

    The project started life 2006 when SABIC formed a partnership with Kayan Petrochemicals and announced that it was planning to build the world’s largest integrated petrochemicals facility in Jubail Industrial City on the shores of the Arabian Gulf. 

    The project was refinanced in 2008 in a $6 billion deal with a number of banks in a move to diversify the sources of finance. Saudi Kayan also took a $533m loan from the Saudi Industrial Development Fund to complete the construction costs. 

    As well expanding the range of products produced in Saudi Arabia, Saudi Kayan intends to establish an applications centre which will focus on the development of industrial products and applications.

    8.                  Hassyan Power & Desalination Plant (UAE)

    Client: Dubai Electricity and Watar Authority (DEWA)
    Scope: Construction of six stations with a capacity of around 1500 MW (gross) power & 100 - 120 MIGD desalinated water with a configuration plus a water storage and transfer system.
    Status: Work scheduled to begin early 2010
    Estimated Cost: $8.6 billion
    Known Contractors: Project out to tender

    Demand for power and water in Dubai is continuing to rise steeply as a result of the Emirate’s burgeoning economy and growing population.
    As a consequence, state-owned utility Dubai Electricity and Water Authority (DEWA) has begun building one of the largest power and desalination plants in the world which, upon completion, will produce 9,000 MW of power and 720 million gallons of water each day.

    The plant is being built on a 4 km2 site 60 km south-west of Dubai City on the shores of the Arabian Gulf. Nakheel’s Dubai Waterfront development is under construction to the north of the site and the border with Abu Dhabi lies to the south.

    The plant will be built in six stages with the first two stages, PI Station and PII Station, due online from 2012. PI and PII will each consist of a 1,500 MW combined cycle gas power island and a 120 MIGD (million imperial gallons per day) desalination island. Costs are estimated at $2 to 3 billion per stage. Later stages of the plant are planned to come online from 2013.

    A seawater intake canal carrying 90,000 gallons of water each second runs along the northern length of the site providing each of the six stages of the plant with water for desalination and cooling. Construction of the canal begins in 2009 and involves extensive dredging and civil works including the building of a 1.5 km long offshore intake channel and a 4 km long onshore canal. In addition, an offshore outfall channel will be built for the discharge of cooling water and brine from the plant. The outfall channel ends 4 km out to sea so that warm discharged brine is not re-circulated into the intake channel.

    9.                  Ras Girtas Power Project (Qatar)

    Client: Qatar General Electricity & Water Company
    Scope: 9000 MW and 340 million imperial gallon per day (MIGD) targeted capacity when complete
    Status: Project scheduled to start production in 2010 and in  2011 initially with 2730 MW of power and 63 MIGD of water
    Estimated Cost: $3.9 Billion
    Known Contractors: Mitsui Corporation of Japan, Hyundai Engineering and Construction Company, Mitsubishi Heavy Industry, Sidem.

    Qatar's non-hydrocarbon economy is booming on the back of its gas investments and infrastructure developments. Population growth and increasing economic diversification will put a strain on current power and desalination capacity, so this project is key to the continued economic expansion of Qatar.

    Qatar’s stable financial position and political environment, government support for investment, and availability of legislation and guarantees had contributed to the confidence of local and international banks in financing local projects, such as the Ras Girtas Project.

    Careful consideration had been given to minimise and control emissions from the plant to meet international levels and standards and the government recently said it was comitted to completing the project on time, within allocated budgets and with a high level of quality and safety standards.

    Once complete the plant will also provide off-peak electricity to neighbouring GCC countries via a planned regional power grid.  

    The project is a Joint Venture between Qatar Petroleum (15%), Qatar Electricity and Water Company (45%), GDF Suez of France (20%), Mitsui Corporation of Japan (10%), Chubu Corporation of Japan (5%) and Shikoku Corporation of Japan (5%). "
      
    10.              Shaybah Phase 2 Expansion (Saudi Arabia)

    Client: Saudi Aramco
    Scope: 250,000 bpd extra oil capacity
    Status: Almost completed, due to start production June 2009
    Estimated Cost: $3 billion
    Known Contractors: SNC-Lavalin, Hyundai Heavy Industries (HHI), Energy and Power Contracting Co, Haif Co, Ahmad Al-Binali and Sons.

    The Phase 2 expansion of the remote Shaybah oilfield, located in Saudi Arabia’s Empty Quarter has been quietly gaining momentum for the past five years. The completion date was supposed to be 2008 but work on the project slowed during 2008 due to a drop in global oil demand.

    The project involves the construction of central processing facilites, including gas/oil separation plant, gas compression facilities, utilities, a gas turbine generation plant and electrical facilities. It has been reported recently that the project, which will increase the Shaybah’s capacity by 250,000 barrels per day (bpd) should be finished ‘within weeks’. The expansion will give Shaybah an output capacity of 750,000 bpd of Arabian Extra Light crude.