Environmental Engineering Reference
In-Depth Information
In the early days of its application in process plants; people were triggered with its
capability in such direction, hence many plants have been reporting successful applications.
In many other cases realizing all possible potential in energy consumption collided with
excessive needs for capital investment. In case of the oil and gas separation presented in this
paper, Figure 2 below shows that for hot and cold streams minimum approach temperature of
17 ºF, the one used in the base case design, minimum heating and minimum cooling utilities
consumption due to heat integration are 615 and 24 MM Btu/h respectively. Heating oil
media is used to render the desired heating and air is used for the desired cooling. Realizing
such results needs significant capital investment and the decision makers are always looking
for scenarios to select among it, where they get highest possible impact on energy
consumption and GHG emissions reduction with minimum capital investment.
A furnace with about 90 percent efficiency is used to heat up the return hot oil and
electricity is taken from the grid to supply for air coolers and others. This furnace will
produce about 300 kg of CO
2
per hour for each megawatt of heat delivered to the heating oil
media used in the process [1].
It is important to note here that even though the hot oil system used in the process can
better match the process requirements for heating purposes compared with steam due to the
slope of the heat deficit curve, as per the shown grand composite curve in Figure 3.In early
design stages it might be much better to consider cogeneration application. Considering a
CHP combined heat and power system in oil and gas separation processes can produce the
desired electricity for the plant and the low pressure steam produced as a by-product of the
cogeneration system in process heating purposes.
In this chapter the HEN design is only considered and not the whole utilities system.
According to pinch technology heuristics for defining the minimum number of units, we have
8 streams above the pinch and 3 streams below the pinch, eleven heat exchangers will be
required. This number can increase and form a very complex network in order to satisfy the
desired energy targets for the oil and gas separation system while the base case design
network is using only seven heat exchangers. Enabling the process owners to exercise their
best budget allocation in reducing energy consumption and GHG emissions by a little defined
increase in the capital investment is shown in the graphs below.
In figure 4 below only one heat exchanger has been added to the base case design to
integrate the discharge of the first stage compressor with a branch from the crude stream
before the desalter. In addition to the relocation of the stabilizer bottoms feed heat exchanger
to make the matching happens before the desalter instead of having it after the desalter. This
change requires an increase in the reboiler duty from the base case design of 197 MM Btu/h
to 272 MM Btu/h
Such modifications in the base case design due to better integration results in about 85.8
MM Btu/h savings in heating oil duty and about 180 T/d reductions in GHG emissions and
of-course savings air cooling duties savings too.
The capital investment is exhibited in the extra heat exchangers surface area increase
shown in graph below.
