AS_6

CONTROLLO

tecnica

Settembre 2017

Automazione e Strumentazione

The benefits of implementing Advanced Process Control applications on secondary

units and networks are significant from both a margins increase perspective and

an operational excellence perspective. However, due to a lack of understanding of

achievable benefits, shortage of APC resources and gap in APC technology, among

other reasons, some organizations do not expand their APC footprint, leaving

significant benefits on the table. Some APC examples are discussed in the paper.

Stefano Lodolo

Tushar Singh

Capturing APC Benefits

from Secondary Units

Advanced Process Control

(APC) has been

used in the process industry and in various

forms for many decades. From DCS-based

primary control schemes and computer-based

Multivariable Predictive Control

(MPC), to

a wide variety of process units such as atmos-

pheric and vacuum distillation units, conversion

units (hydrocracker, FCC, coker, visbreaker),

hydrotreaters, gasoline reformers and often

some other units like isomerization, steam

reformers and distillation trains. While many

organizations focus only on major process units,

the best in class ones

expand APC footprint to

secondary

units to achieve additional benefits.

This may include APC for environmental emis-

sions control, fuel gas network control, sulphur

complex control, steam networks control, H2

networks control and more.

Environmental Emissions Control

In a typical refining or petrochemical site both

Fuel Oil (FO) and Fuel Gas (FG) are com-

busted in some furnaces or boilers. Analyzers

are available at furnace level (typically O2, CO)

while others are available at stack level (typi-

cally SOx, NOx) with multiple furnaces send-

ing flue gas to the same stack.

Ideally, facilities would have a system in place

that would measure the environmental limits

in the furnace and stack level, however due to

the local, regional and specific country regula-

tions, the process to respect these limits can be

extremely complicated. Limits tend to become

more and more stringent over time, they may

apply for dust, CO, NOx, and SOx for both con-

centration and mass and they sometimes apply

to single furnaces, boilers, single stacks and/or

the overall site. Moreover, these limits are not

to be applied ‘as-is’ and rules like “(97% of 48h

averages) < (LIMIT * tolerance)” often apply.

In addition, to make things more complicated,

limits are actually changing depending on the

fuels mix, e.g. the FO/FG ratio.

Given the above complexity, operators typi-

cally only control the real-time measure, taking

a huge safety margin compared to what an APC

system can do. This leaves on the table a rele-

vant amount of money that could be measured

GLI AUTORI

S. Lodolo, Senior Advisor, Aspen-

Tech; T. Singh, Product Marketing

Manager, AspenTech

IMPROVEMENTS IN ADVANCED PROCESS CONTROL IMPLEMENTATION

Raccogliere i benefici del controllo avanzato sugli impianti

secondari

Nell’articolo sono discussi i benefici dell’utilizzo di strategie di controllo avanzato sugli impianti secondari e sulle reti di processo. I benefici

realizzabili in queste aree sono significativi ma spesso la limitata comprensione delle specifiche problematiche, la carenza di risorse di

Controllo Avanzato ed i gap nella tecnologia di Controllo Avanzato utilizzata, limitano le applicazioni. Nell’articolo vengono presentati alcuni

esempi che hanno consentito di raggiungere significativi risultati economici ed operativi in quest’area.