Page 221 - Sustainability in the process industry

198 Cha p te r N i n e

fuel and type of combustion device to generate targets for emissions
of CO , SO , NO , and particulates. It is then possible to explore the
2 x x
various options for reducing these emissions.
9.3.4 SITE-int

Like HEAT-int (see Section 9.3.2), SITE-int (2009) is a product of
Process Integration Ltd. SITE-int is a state-of-the-art software package
for the design, optimization, and integration of site utility systems in
process industries. Its main features include methods to: (1) model
and optimize site utility systems; (2) minimize operating costs for
existing systems without modification; (3) target cogeneration
potential; (4) optimize site steam pressures and loads; (5) minimize
site energy costs through system modifications; (6) determine the
true benefit from saving energy in the individual processes; (7) reduce
greenhouse gas emissions from the site; and (8) create partial-load
models of utility system components from plant operating data using
regression functions and data reconciliation functions.

9.3.5 WORK
WORK is the software package used for the design of low-temperature
(subambient) processes (WORK, 2009). Low-temperature processes
require heat rejection to refrigeration systems. As a result, the
operating costs for such processes are usually dominated by the cost
of power to run the refrigeration system. Complex refrigeration
systems—including cascade and mixed refrigerant systems—can be
analyzed using WORK. For mixed refrigerants, WORK can be used
to optimize refrigerant composition. The software enables the user
to: (1) understand complex refrigeration systems; (2) target minimum
shaft work for low-temperature cooling duties; (3) optimize the
number and temperatures of refrigeration levels; (4) target minimum
shaft work for cascade refrigeration systems; (5) target minimum
shaft work for mixed refrigerant systems; and (6) determine the
optimum composition for mixed refrigeration systems. Three of
these features are discussed in more detail next.
Targeting low-temperature systems: WORK can target minimum
shaft work for simple and complex refrigeration cycles. Targets are
based on rigorous thermodynamic calculations that are highly
accurate even when compared with the results of rigorous simulation.
When multiple refrigeration levels are used, trade-offs arise between
temperature levels and shaft loads. Adjustments to each temperature
level affects not only its own shaftwork requirement but also that of
the other levels. Therefore, all levels of refrigeration must be
optimized simultaneously. This task is facilitated by WORK’s
extremely accurate shaftwork predictions.
Simulating refrigeration systems: WORK enables the simulation of
simple and complex refrigeration systems (see Figure 9.5), which may
involve multiple heat levels and multiple compressors. The refrigerant