Further Reading
5.6 Answer Key
Section 5.1.1. The void fraction is a dimensionless parameter. The suggested formulation results in dimensions of (length)−0.25 due to the presence of the diameter in the second term of the denominator of the equation. For laboratory‐scale systems, pipe diameters are generally small, and the error from the suggestion may be negligible. However, in commercial‐scale facilities the error can be significant.
Section 5.3.1. For reboiler elevation 4.72 m below tower bottom tangent line; pressure drops exclude the reboiler.
1. 487 348 kg/h.
2. Segment 1: 2 90° bends, 1 branch T, 1 entrance, 11.7 m straight length at reboiler elevation =
−6.2 m from tangent line; total equivalent length = 61.2 m. Segment 2: 1 90° bend, 1 gate valve, 1 exit, 3 m straight length; total equivalent length = 37.9 m.
3. Friction loss: 1.5 kPa; Static rise: 30 kPa.
4. Exit pressure: 1.305 MPa.
Section 5.3.2. For a reboiler elevation 4.72 m below tower bottom tangent line, pressure drops including the reboiler:
5. Liquid only: 6.28E‐03 kPa/m; Gas only: 9.04E‐02 kPa/m.
6. Segment 1: 55.5 m, Segment 2: 85.6 m.
7. Segment 1: MSH = 6.04E‐2 kPa/m, 4.0 kPa total friction loss. Segment 2: MSH = 5.17E‐2 kPa/m, 5.3 kPa total friction loss.
8. ε = 0.78.
9. Segment 1: 127.5 kg/m3 loss = 2 kPa; segment 2: 126.6 5 kg/m3, loss = 10 kPa.
10. Total pressure loss = 23 kPa.
11. Reboiler centerline 4.72 m below tower bottom tangent line.
12. Tower elevation 7.94 m (4.72 + 1.22 + 2).
Section 5.3.3
13. NPSHR = 0.84 m including the safety margin.
14. Minimum tower tangent line elevation 1 m.
15. Tower elevation set by the reboiler. Available NPSH = 6.2 m.
References
Abdulmouti, H. (2014) Bubbly two‐phase flow: Part I‐ characteristics, structures, behaviors and flow patterns.
American Journal of Fluid Dynamics 4(4), 194–240.
Crane® (1988) Flow of Fluids Through Valves, Fitting, and Pipe. Technical Paper No. 410. Crane Co., Joliet, IL.
Ding, C., Carlson, L., Ellis, C., and Mohseni, O. (2005) Pressure Loss Coefficients of 6, 8 and 10‐inch Steel Pipe Fittings, University of Minnesota St. Anthony Falls Laboratory, Minneapolis, MN, http://conservancy.umn.edu/
bitstream/handle/11299/113368/pr461.pdf?sequence=1(accessed January 24, 2016).
Müller‐Steinhagen, H. and Heck, K. (1986) A Simple Friction Pressure Drop Correlation for Two‐Phase Flow in Pipes, Elsevier, Amsterdam.
Project Management Institute (2013) Project Management Body of Knowledge. 5th edn. Project Management Institute, Inc., Newtown Square, PN.
Serghides, T. K. (1984) Estimate friction factor accurately. Chemical Engineering 91(5), 63–64.
Taitel, Y. and Dukler, A. E. (1976) A model for predicting flow regime transitions in horizontal and near horizontal gas‐liquid flow. AIChE Journal 22(1), 47–55.
Thorne, J. R. (2006) Engineering Data Book III, Wolverine Tube Inc., Decatur, AL, Chapter 13, http://www.wlv.com/
wp‐content/uploads/2014/06/databook3/data/db3ch13.pdf (accessed January 24, 2016).
Woldesemayat, M. A. and Ghjar, A. J. (2006) Comparison of void fraction correlations for different flow patterns in horizontal and upward inclined pipes. International Journal of Multiphase Flow 33, 347–370.
Case Studies in Mechanical Engineering: Decision Making, Thermodynamics, Fluid Mechanics and Heat Transfer, First Edition. Stuart Sabol.
© 2016 John Wiley & Sons, Ltd. Published 2016 by John Wiley & Sons, Ltd.
Companion website: www.wiley.com/go/sabol/mechanical
Reliability and Availability
Liquefied natural gas (LNG) provides a means to transport natural gas across great distances without pipeline infrastructure. Those countries and regions of the world without abundant natural‐gas resources often import it in the form of LNG via ship. Liquefied natural gas is primarily methane with varying quantities of heavier hydrocarbon impurities, depending on its source and the specific requirements for transportation of the vaporized liquid, cooled to a liquid state. Transportation of the liquid phase via specially designed ships makes it possible to receive a clean‐burning energy source competitive with other fossil fuels, renewable energy, and nuclear power sources in regions that lack natural resources.
Countries in the Orient, Japan, and Korea for example, import significant quantities of LNG from around the globe, including Africa, the Middle East, Australia, and North America.
Liquefaction facilities compete for market share using price, contract terms, LNG quality, and so forth, to secure supply contracts with perspective buyers.
Your company has been commissioned to design and build an LNG import terminal. The terminal will involve dredging the harbor to accommodate the large LNG tankers, a new berth- ing facility, offloading equipment to remove the LNG from the tankers, LNG storage facilities, regasification equipment to convert LNG to natural gas, compression equipment to supply the regasified LNG into transcontinental pipelines, and 50 km of pipeline laterals to connect the facility to existing transcontinental pipelines. Stakeholders in the project include the national government, the local harbor master, local communities, shipping companies, suppliers of LNG, and natural gas customers.
Compression of the regasified LNG into the pipelines will require a significant amount of power. Liquefied natural gas is stored at atmospheric pressure in large insulated tanks. From the storage pressure, the natural gas must be compressed to approximately 6.9 MPa to meet the pipeline requirements. As the import terminal is located in a remote location, a new power
Case 6
plant is included in the project. Waste heat from the power plant will supply the energy required to regasify the LNG. Excess electricity produced will supply the local market as a byproduct.
The project has a requirement to meet 98% regasification availability on an annual basis.
That is, the regasification facilities should be able to provide the full design capacity of natural gas to the pipeline for all but 175 hours during a year – about 1 week. Unexpected outages or curtailments in production would result in penalties itemized in sales and delivery contracts.
To meet the project’s economic targets, the waste heat supply from the power plant should have an availability greater than the 98% target.
Prior to submitting a proposal for the power plant and waste heat supply, a verified calculation of the power system heat supply availability is necessary.