Thesis - Oztek_Muzaffer_T_200508_MA

1. INTRODUCTION
The focus of this study is the separation of hydrogen helium mixtures formed at
the Kennedy Space Center (KSC), where hydrogen is used as fuel for the space shuttle
main engines, as well as in the fuel cells, and helium is used as the purge gas. The waste
purge gas is one of the two different kinds of hydrogen loss at the center. The other is the
loss of hydrogen from boil off from the liquid.
A major loss of hydrogen from boil off occurs when liquid hydrogen brought by
trucks and rail cars is transferred to storage dewars via insulated pipelines and from
storage to the necessary units such as fuel tanks. In this process, loss of hydrogen occurs
through
• Cooldown of the vacuum-jacketed lines
• Flash evaporation as high pressure liquid enters the low pressure dewar
• Cooling of the inner skin of the dewar with the rising liquid
• Displacement of the gas above the liquid in the ullage space.
The waste gas is vented to the atmosphere or burned. This boiled off gas is pure hydrogen
and its recovery has been studied previously[1].
The flash evaporation of hydrogen as pressure decreases from a tanker transfer
pressure of approximately 0.26 MPa (2.57 atm) to a dewar storage pressure of 0.12 MPa
(1.18 atm) is the step in the hydrogen transfer that incurs the greatest amount of loss. It is
also identified as the most cost effective and readily recoverable loss [2]. It was estimated
that 1.5 million gallons (5.68 x 10 3 m 3 ) of liquid hydrogen can be recovered. A total of
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