Pipeline capacity and economics

Gas pipeline construction: calculating the pipe diameter, the pressure required for the transportation of natural gas compressors. The definition of capital costs for construction and operation of the pipeline. Financial management of the project.

Рубрика Экономика и экономическая теория
Вид статья
Язык английский
Дата добавления 05.12.2012
Размер файла 774,7 K

Отправить свою хорошую работу в базу знаний просто. Используйте форму, расположенную ниже

Студенты, аспиранты, молодые ученые, использующие базу знаний в своей учебе и работе, будут вам очень благодарны.

Размещено на http://www.allbest.ru/

PIPELINE CAPACITY AND ECONOMICS

INTRODUCTION

In the construction of natural gas transmission pipelines a lot of things should be considered. For example pipe sizes, the pressure required to transport natural gas from one location to another and the pressure drop that will proceed. To accurate this, compressors are required which need to be sized for the compression requirements. In addition Pipe loops will be designed that increase the capacity of the pipeline by adding theoretical diameter.

Pipelines are planned to integrate into existing networks and are constructed to transport a company's own natural gas, to transport natural gas through an owned section of pipeline for another company, or to transfer the ownership of natural gas to another and into their assets (pipeline). For these 3 permutations in operation investment in the infrastructure and assets will be made to a varying degree while meeting all of the regulation requirements to ensure that the safe operation and environment considerations have been made.

To meet the capital requirement (CAPEX) for developing pipelines, companies have to provide strong business cases in how the financing and remuneration through operation will be managed. The budget for pipeline development will be determined by the capital costs of the planned length of pipeline and operational term in service. Some of the elements of the capital costs are as follows:

1. Pipeline

2. Compressor stations

3. Mainline valve stations

4. Meter stations

5. Pressure regulator stations

6. SCADA and telecommunication

7. Environmental and permitting

8. Right of way acquisitions

9. Engineering and construction management

PIPELINE CAPACITY AND ECONOMICS

In the design and planning of the physical pipeline systems several variables are to be considered. The majority of these variables come from the general flow equation which is determines the daily capacity of a gas pipeline:

Using this equation produce derivative equations to illustrate the relationship with some of the variables and how impact on the overall capacity of the pipeline on a daily basis. This is shown as a capacity factor or as volumetric capacity for daily deliverables. In conditions of overall economical potential the pipeline capacity as earlier mentioned is a important factor in determining the transportation price and hence the capital recovery for investment in projects of this nature.

One of the capacity functions are:

1. Inlet pipe pressure

2. Pressure drop

3. Pipeline diameter

4. Pipeline Length

INLET PRESSURE

Use the derivative equation below the illustration of variation of inlet pressure in stages of 10 bar for a standard pipe diameter with a constant pressure drop ?P of 20 bar can be seen.

For this arrangement we can use the formula:

Q ?

This allows us to determine the capacity factor CF which is a function of the inlet pressure.

Table 1

Effect of Inlet pressure on pipeline capacity

Q

?P

P?

?P(2P? -?P)

CF

20

0

-400

0

20

10

0

0

20

20

20

400

1

28.28427

20

30

800

1.06066

34.64102

20

40

1200

1.154701

40

20

50

1600

1.25

44.72136

20

60

2000

1.341641

48.98979

20

70

2400

1.428869

52.91503

20

80

2800

1.511858

56.56854

20

90

3200

1.59099

63.08724

20

100

3980

1.585107

Figure 1. Pipeline capacity increases with increased inlet pressure

From figure 1 any increase in inlet pressure for a standard pressure drop of 20 (bar) will increase the capacity of the pipeline. There is a rapid increase in capacity between 10-20 (bar) and then a uniform or linear increase between 30-90 (bar) for inlet pressure. Standard systems will use the linear increase in capacity as they will require a pressure drop in the system to be able to transmit efficiently. In terms of transmission pressures the majority of pipelines in the UK will transmit around 65 (bar) which is in the range of linear capacity building in pipelines.

Also using an example for a pipeline of fixed dimensions we can explore further the original equation by producing the derivative equation.

Where:

P1 (inlet pressure) is varied in stages of 10 bar

P2 (outlet pressure) is a function of the pressure drop known to be 20 bar for the system.

D is the diameter of the pipeline (30'' or equivalent to 750mm DN)

L is length of a standard section of pipeline taken to be 48km

EXAMPLE CALCULATION

Q ? x = 217.855 capacity (mill m3/ day)

Table 2

Inlet pressure varied in stages of 10 bar

p1

?P

p2

d

L

Q ?

10

20

-10

750

48

0

20

20

0

750

48

44469530

30

20

10

750

48

62889412

40

20

20

750

48

77023485

50

20

30

750

48

88939059

60

20

40

750

48

99436891

70

20

50

750

48

1.09E+08

80

20

60

750

48

1.18E+08

90

20

70

750

48

1.26E+08

100

20

80

750

48

1.33E+08

110

20

90

750

48

1.41E+08

120

20

100

750

48

1.47E+08

130

20

110

750

48

1.54E+08

140

20

120

750

48

1.6E+08

150

20

130

750

48

1.66E+08

160

20

140

750

48

1.72E+08

170

20

150

750

48

1.78E+08

180

20

160

750

48

1.83E+08

190

20

170

750

48

1.89E+08

200

20

180

750

48

1.94E+08

210

20

190

750

48

1.99E+08

220

20

200

750

48

2.04E+08

230

20

210

750

48

2.09E+08

240

20

220

750

48

2.13E+08

250

20

230

750

48

2.18E+08

Figure 2. Potential capacity increase for inlet pressure increase

PRESSURE DROP

The effect of pressure drop on pipeline capacity for a fixed inlet pressure can also be calculated from the derivative of the General Flow Equation.

Where, Q ? v (P12-P22) with a fixed inlet pressure and variation of pressure drop.

SAMPLE CALCULATION

v (702-502) = 48.99

Table 3

Uniform pressure drop in stages of 5 bar

Q

p1

p2

?P

CF

0

70

70

0

0

25.98076

70

65

5

0.53033

36.05551

70

60

10

0.73598

43.30127

70

55

15

0.883883

48.98979

70

50

20

1

53.61903

70

45

25

1.094494

57.44563

70

40

30

1.172604

60.62178

70

35

35

1.237437

63.24555

70

30

40

1.290994

65.38348

70

25

45

1.334635

67.08204

70

20

50

1.369306

68.37397

70

15

55

1.395678

69.28203

70

10

60

1.414214

69.8212

70

5

65

1.425219

70

70

0

70

1.428869

Figure 4. Capacity reduction after 20 bar

For gas, we can see by increasing the pressure drop there is a gradual decrease in capacity. We base this prediction by looking at how the capacity behaves before and after the standard pressure drop of 20 bar.

While before the standard pressure drop of 20 bar, in the early region on the graph between 0 - 10 bar there is an uniform increase in capacity. This steadily declines towards the pressure drop of 20 bar and beyond it. As the pressure drop increases the capacity steadily decreases to the point whereby at pressure drop of 70 bar there is no apparent increase in capacity at all.

DIAMETER

The affect the diameter has on the pipeline is quite apparent. As the pipelines diameter increases so does the capacity of that pipeline to hold potentially higher volume of gas or other hydrocarbons. This is because the dynamic viscosity of the gas increases due to greater width of pipeline boundary layers.

As gas is a compressible fluid it tends to be able to be `packed into' pipelines of higher theoretical diameter in methods such as re-enforcement for line packing technique.

This relationship is proven through the derivative of the general flow equation:

Where Q ? d 2.5

For the Midcontinential pipeline example which is comprised of 3 sections:

1. 48km of 30 inch pipe (750mm)

2. 317km of 36 inch pipe (900mm)

3. 442km of 42 inch pipe (1050mm)

This is evident that the planning is to allow an increase in capacity along the run of the pipeline. Calculations show how the capacity gained quite considerably along the run of the pipeline.

Table 4

Diameter driven capacity increase

CF(capacity factor)

Q(volume)

d (DN mm)

1

15404697

750

1.577441

24300000

900

2.319103

35725083

1050

Figure 5. Diameter driven capacity increase

From the graph of Midcontinential gas pipeline we can say that will increase in capacity factor from pipeline section to section. This corresponds to an increase of 1.5 from the 750mm section to 900mm section and an increase in capacity of 2.3 times from the 750mm to 1050mm section. This increase in capacity is used over ranges of 317km and 442km respectively and highlights how the capacity of 48km would most probably be for a feed in for the major transmission line and their potential to increase capacity.

Therefore the higher the diameter the more suitably cost effective it is to transport the gas from region to region. This would generally be used for the interstate (zone) relaying of gas on a national network. The pipelines would be designed to be used in rural locations due to the design factor for safety involved. However the increased costs of laying large diameter pipelines are generally offset by the increased capacity of these lines in years to come. This returns to the premise that most gas pipeline operators will design the network to efficiently yield the maximum capacity possible over the lifetime of the pipeline with planned increase designed in which will allow them to optimize the capacity of the pipeline and gain the maximum transportation tariff for the network within prescribed remuneration limits.

LENGTH

The capacity of the pipeline can be also fluctuate when the length of the pipeline is varied. For example in the 3 section pipeline which connects the Midcontinential pipeline with the Transcontinental pipeline in the USA, the variation in length needs to be determined for each section for optimization of capacity in operation.

For the total pipeline, which is planned, there is a current span of pipeline which is accumulated from;

Section 1 (442km), section 2 (317km), and section 3 (48km)

This gives an overall span of 807km of pipeline of diameters varying from 30''(750mm DN) to 42'' (1040mm DN).

To look at the varying economic trade off from this we can take one section of the pipeline e.g. Section 3 (48km) and vary the length of this pipeline to illustrate.

Table 5

Length as an inhibitor to capacity

Length (km)

CF

20

0.223607

24

0.204124

28

0.188982

32

0.176777

36

0.166667

40

0.158114

48

0.144338

52

0.138675

56

0.133631

60

0.129099

64

0.125

68

0.121268

72

0.117851

76

0.114708

80

0.111803

Figure 6.The effect of pipeline length on capacity

From this graph we can see that as with the drop in capacity the curve provided has the appearance of a declining semi parabolic. The red line indicates the minimum losses in capacity for an achievable span of 20km. However in planning if this length of pipeline were to be undertaken additional costs may be incur in permits and choice of pipeline to meet with design factor needed by the location, if in proximity to population and planning of the pipeline. There will always be an economic and capacity trade off.

If we take the midpoint of this curve (as a point of reference to where the optimum distance should occur knowing that pipeline cost increases and capacity factor decreases less steadily beyond this point) we should find the optimum length of pipeline length to capacity factor. gas pipeline financial capital cost

From the graph this comes to a value of 44 km whereas the actual section under investigation is the 48 km pipeline. The differences in actual planning a pipeline of this length may be down to a number of factors such as costs in negotiating terrain, environmental permits, location of pipeline to dwellings, suburban limits etc. However effectively the most economical length of pipeline would be achieved post the 44 km length as this is when the rate of decline in capacity begins to tailor away. Additional to these factors, as with the other variables, there is an amount of tolerance to the planned length.

COMPRESSOR STATIONS

Compressor stations and compressors generally added to a pipeline to increase capacity. By adding these units at strategically placed intervals in the pipeline the pressure drop in the pipeline is rectified in order to maintain a responsible pressure for further transmission. Pressure drop occurs naturally through the frictional forces in the pipeline which are ever occurring even though some major pipelines are fitted with an epoxy coating to minimize friction. An additional, the major contributor to pressure loss is when terrain inflicts a gradient in the pipelines design. In designing a compressor station along a pipeline consideration must be given to achieve efficiency in the design.

Usually a compression ratio of around 1.5 is acceptable. Thus design factors are considered to try to reduce power input to maintain this level of compression ratio. Effectively today, equipment such as centrifugal compressors are seen as the most efficient in compressing gas however the cost of running this sort of plant has high fuel costs. Therefore there is always a trade off between the economic implications of designing compressor, which are of a high capacity, to maintaining a high capacity in the pipeline. These points will be investigated further.

Compression stations work as a function of the pressure drop and as so will be designed and positioned as a corrective measure as shown in the diagram below.

In the diagram above the intermediate compression station is placed at the half way point between the source location and the end location. However the pressure drop in pipelines is generally non-linear so this is only a theoretical positioning. Further adjustments on the compression stations position will be made by adjusting the compressor ratio in accordance with the end location. Also to ensure that the compressor works efficiently and any costs that are used up in compressing the gas back to a satisfactory transmission pressure will be justified. If the compression station is placed too close to the end location then two things will happen.

Размещено на http://www.allbest.ru/

Figure7. Incremental compressor arrangement

In addition, adjust the discharge pressure of the compression station so that the gas reaches the required pressure at the end location. Or we will have to move the compression station further upstream so that the pressure drop is able to decline the discharge pressure suitably to the end pressure.

Calculations to acquire a suitable location for compressor station are made on a trial and error basis using the general flow equation.

So the taking a standard value for source pressure P1 and receiving pressure P2 we can assume that the compressor in use will be operating within its capacity:

Initial/Discharge Pressure P1 = 70 bar

Receiving/Suction pressure P2 = 50 bar

?P = 20 bar (standard Optimum)

Compression ratio = P1/P2 = 1.4: 1

Compressor sizing 1.5 (centrifugal compressor)

EXAPLE CALCULATIONS

For the general gas flow equation we can overview a system such as the 48km pipeline in USA and how it could potentially use compressors to enhance flow rate to a location. For this example we estimate that the flow rate to be maintained beyond the end of the pipeline and hence the compression station will be at the 48km point.

Размещено на http://www.allbest.ru/

Figure 11. Practical example of compressor planning

Where, Ts = 288,

Ps= 1.013025,

70,

d = 750mm,

S = 0.7,

L= 48km

T = 288

and Z = 0.85

Q = 0.000575 x x= 163.4 x x

= 1.36 mill m3/day

The daily capacity along the pipeline would be 1.36 mm3/day. To maintain this capacity into the section of 327km pipeline a compression unit could be placed at the end to rectify the pressure drop across the pipeline.

The yearly capacity would therefore be 496.4 million m3/year.

ADIABATIC COMPRESSION

In compression through a closed system, the compression can be considered as adiabatic when it doesn't give any heat off to the surroundings. If the compression is heat efficient, which generally they are, then the size of the compression unit can be calculated from the gas flow (capacity) and the suction pressure and discharge pressure( pressure differential) for the unit.

And the work done is calculated from the equation:

Wa = x T1 [ -1]

We can therefore use the 48km pipeline flow rate and the optimum pressure differential to calculate the number of compressors needed to maintain the flow rate prescribed for the next stage of the transmission line I.e. 1.35 mill m3/day into the 327km section.

A simplified version of the equation for work done discounts any heat lost due to adiabatic process.

Wa = x (288) Loge = 39,162 J/Kg

The volume of gas processed per second can be found by:

1.36 x 10 6 / (24 x 3600) = 15.74 cubic metres of gas/second.

And the weight of the gas is given by 15.74/0.714 = 22.05 kg

Wt, the total work done

22.05 x 39,162 = 863,336.4 J

The total work required to transfer 21.07 kg would be 863.33 KJ.

Further more, we can size the compressor power unit that we need.

Power = 4.0639 x 1.36 ((288) ( =

621.23 kW

The compressor driver may have mechanical efficiency of 98% so

Driver power = = 633.91kW

Sizing the compressor units for Horse Power we can use the equation

HP = 0.0857 x 48.85 ((288) ( = 470.66

HP.

With the mechanical efficiency of the driver taken into consideration as 0.98 we can calculate the break horse power of the unit.

BHP = = = 480.26 BHP

The BHP required to drive the compression operation could be effectively one 500 BHP unit.

Compression units vary in size from 50 BHP up to around 20,000 BHP. This is of the smaller capacity however in further planning it would be recommended to oversize the unit.

CONCLUSION

From the results obtained it shows that due economic analysis must be carried out before pipeline development:

1. Detailed market survey to ascertain peak loads, average and minimum demand of consumers in order to adequately size a pipeline

2. Detailed route survey to ascertain the nearest distance for gas supply to a customer

3. Detailed energy audit of consumer equipment in order for pressure distribution

4. Detailed engineering design to properly cost a pipeline network

With the knowledge of how the above four parameters discussed affects capacity one can properly cost and size adequately a pipeline for either transmission or distribution purpose.

REFERENCE

1. Kadir A., University of Salford, Distribution and Transmission Lecture Notes 2011/12.

2. E. Shashi Menon, Pipeline Hydraulics, Taylor & Francis 2005.

3. Roberts, John.,1996. Caspian Pipelines. The Royal Institute of International Affairs.

Размещено на Allbest.ru


Подобные документы

  • Directions of activity of enterprise. The organizational structure of the management. Valuation of fixed and current assets. Analysis of the structure of costs and business income. Proposals to improve the financial and economic situation of the company.

    курсовая работа [1,3 M], добавлен 29.10.2014

  • Формирование корпоративных структур. Порядок государственного регулирования деятельности. Мировая практика деятельности холдингов. Финансовые показатели, управление, органы управления, факторы роста, управление рисками в АО "System Capital Management".

    реферат [179,4 K], добавлен 24.01.2014

  • Calculation of accounting and economic profits. The law of diminishing returns. Short-Run production relationships and production costs, it's graphic representation. The long-run cost curve. Average fixed, variable, total costs and marginal costs.

    презентация [66,7 K], добавлен 19.10.2016

  • Project background and rationales. Development methodology, schedule planning. Company mission and vision. Organization of staff and company structure. Procurement system target market. Implementation of procurement system. Testing, user manual.

    дипломная работа [6,8 M], добавлен 28.11.2013

  • Financial bubble - a phenomenon on the financial market, when the assessments of people exceed the fair price. The description of key figures of financial bubble. Methods of predicting the emergence of financial bubbles, their use in different situations.

    реферат [90,0 K], добавлен 14.02.2016

  • Natural gas market overview: volume, value, segmentation. Supply and demand Factors of natural gas. Internal rivalry & competitors' overview. Outlook of the EU's energy demand from 2007 to 2030. Drivers of supplier power in the EU natural gas market.

    курсовая работа [2,0 M], добавлен 10.11.2013

  • Analysis of the status and role of small business in the economy of China in the global financial crisis. The definition of the legal regulations on its establishment. Description of the policy of the state to reduce their reliance on the banking sector.

    реферат [17,5 K], добавлен 17.05.2016

  • General characteristic of the LLC DTEK Zuevskaya TPP and its main function. The history of appearance and development of the company. Characteristics of the organizational management structure. Analysis of financial and economic performance indicators.

    отчет по практике [4,2 M], добавлен 22.05.2015

  • The essence of Natural Monopoly. The necessity of regulation over Natural Monopoly. Methods of state regulation over the Natural Monopolies. Analysis and Uzbek practice of regulation over Monopolies. Natural Monopolies in modern Economy of Uzbekistan.

    курсовая работа [307,7 K], добавлен 13.03.2014

  • Resources of income for enterprises. Main ways of decreasing the costs Main ways of increasing the income. Any enterprise’s target is to make profit. In order to make it a company should understand where comes from the income and where goes out costs.

    курсовая работа [59,9 K], добавлен 09.11.2010

Работы в архивах красиво оформлены согласно требованиям ВУЗов и содержат рисунки, диаграммы, формулы и т.д.
PPT, PPTX и PDF-файлы представлены только в архивах.
Рекомендуем скачать работу.