Page 306 - Petroleum and Gas Field Processing

3. Downstream processing requirements. In most commercial
hydrocarbon processes, the presence of water may cause side
reactions, foaming, or catalyst deactivation. Consequently,
purchasers typically require that gas and liquid petroleum gas
(LPG) feedstocks meet certain specifications for maximum water
content. This ensures that water-based problems will not hamper
downstream operations.

12.2 PREDICTION OF HYDRATE FORMATION

In this section, methods for determining the operating conditions leading
to hydrate formation are presented. In particular, methods are presented
to determine the following:
1. Hydrate formation temperature for a given pressure
2. Hydrate formation pressure for a given temperature
3. Amount of water vapor that saturates the gas at a given pressure
and temperature (i.e., at the dew point)

At any specified pressure, the temperature at which the gas is saturated
with water vapor is being defined as the ‘‘dew point’’. Cooling of the gas
in a flow line due to heat loss can cause the gas temperature to drop below
the hydrate formation temperature.
Two methods are discussed next for predicting the conditions leading
to hydrate formation: approximate methods and analytical methods.

12.2.1 Approximate Methods

1st: To determine hydrate formation pressure or temperature. This
method utilizes the chart shown in Figure 1; it involves the
following steps:
1. Calculate the average molecular weight of the gas mixture
M G
2. Calculate the specific gravity of the gas,
G , where
G ¼ M G /
M air .
3. Given the gas temperature (T ) and its specific gravity (
G ),
find the corresponding gas pressure for hydrate formation
using Figure 1.
4. Similarly, at a given gas pressure, the hydrate formation
temperature can be determined from Figure 1.

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.