(186c) Cleaning Heat Exchangers: How, When, Where and How Much?

Authors: 
Lanchas, L., Imperial College London
Francia, V., Hexxcell Ltd.

AIChE Spring Meeting 2016

ABSTRACT

Cleaning heat exchangers: how, when, where and how much?

Laura Lanchas-Fuentes,
Emilio Díaz-Bejarano, Sandro Macchietto and Francesco Coletti*

Hexxcell
Ltd., Imperial College Incubator, Bessemer Building Level 2, Imperial College
London, SW7 2AZ (UK)

* Corresponding author: f.coletti@hexxcell.com

Energy recovery and
production in oil refinery pre-heat trains are greatly affected by fouling, the
progressive build-up of unwanted material on the heat exchanger surfaces. Even
when good design and operating practices are followed and mitigation technologies
are in place, very often crude oil fouling cannot be completely eliminated. As
a result, it is necessary to carry out periodical cleaning of the heat
exchangers.

Refineries typically
use two methodologies to clean their heat exchangers: mechanical (e.g.
hydro-blast) and chemical cleaning. Chemical cleaning methods represent a quicker
and cheaper, though less effective, option than the more commonly used
mechanical ones. They allow cleaning a heat exchanger in place, removing the
need to open the shell and pull the bundle, thus significantly shortening the
downtime. However, they typically return the exchanger to operations in a less
clean condition. If the chemical used is ineffective, not only the benefits of
a faster turnaround time can be lost, but the overall costs to the refinery may
increase. To accurately assess the overalle economic benefits for the different options, it is therefore important
to capture the trade-offs between the effectiveness of the cleaning action and
the offline time required for it.

In this paper, the
advantages and disadvantages between chemical and mechanical cleaning methods
are discussed. Hexxcell Studio™, a
thermo-hydraulic fouling analysis and prediction simulation software, is used to
assess the impact of and techno-economic trade-offs between cleaning options.
This cleaning analysis includes:

i)                    
Establishing the
effectiveness and depth of cleaning achieved by different chemical cleaning
agents and the exchanger conditions left at the end (which depend on the
deposit state prior to the cleaning and cleaning time). These will also affect
fouling build-up in subsequent operation.

ii)                  
Minimising the cleaning
time for a specific chemical cleaning agent (which we term “condition-based
cleaning”)

iii)                 
Calculating the detailed
interaction effects that cleaning individual exchangers has on the fouling,
heat duty and pressure drop of other exchangers in a network and overall

iv)                 
Generating
alternative cleaning schedules involving the selection of the appropriate type
of chemical and mechanical cleaning, and assessing the cleaning schedule performance
based on thermal and hydraulic considerations, costs of energy and refinery
margins.

Results are
presented using an industrially relevant case study.