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NAME ___________________ SIGNATURE _____________________ UT EID ___________________ MIDTERM EXAM PGE 421K SPRING 2009 Open book and open notes. Answer all seven questions on the exam paper. If you think you need more information to solve a problem, make a plausible assumption, write it down, and continue working. No credit for answers with inappropriate units. 1) A group of investors seeks your advice on the feasibility of a natural gas storage project. The idea is to pump water from a relatively shallow aquifer (800 ft deep, contains 1.5 wt % NaCl, density = 1015 kg/m 3 ) and inject it into a thick, areally extensive salt formation (4200 ft deep). The water dissolves the salt until it reaches saturation, and operator then extracts the salt-saturated brine. In this way the operator will create a large cavern in which natural gas can be stored. Design specifications include: 20 points Helpful constants 379 SCF = 1 lb mol salt = 2150 kg/m 3 Gas storage capacity in a single cavern is 10 BCF. Molecular weight of the natural gas is 16.8 lb/lbmol. Salt formation has a temperature of 48 C. When filled with natural gas the pressure in the cavern should be no greater than 1470 psia. At storage conditions, the natural gas may be regarded as an ideal gas. The concentration of NaCl in the salt-saturated brine is 25 wt %. The density of the NaCl-saturated brine is 1150 kg/m 3 a) Sketch a control volume that will be useful in answering parts (b) - (d) 1
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minimum volume of salt that must be removed for one cavern? 2
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