In the future, increased demands for high-quality fresh
water supplies will translate into voluntary and, ultimately,
regulatory mandates. These constraints will require facilities to limit or to reduce
withdrawal volumes from the local watershed. Plant personnel in
southeast Texas have been living this scenario as a severe
drought continues to compromise the quality and
quantity of fresh water. However, implementing
temporary solutions is not the same as crafting permanent
A reasonable approach.
Water-reuse projects are typically long-term efforts. They
require a significant amount of analysis before making any
capital project commitments. The initial
efforts will require participation by a broad range of
personnel: technical service, operations, water treatment
suppliers and outside experts.
Optimize present utility/process water systems.
This step is considered a low-hanging fruit action
item: reducing water usage that requires minimal analysis and
operational changes with little or no capital investment. Your
chemical supplier may be willing to assist in identifying
opportunities to improve system reliability with innovative
treatment strategies. Typical examples include excessively long
times for the final rinse of softeners and demineralizers, low
recovery rates for reverse osmosis and high blowdown rates in
Construct a water and wastewater balance.
Most plants have a validated steam balance, but few facilities have an analogous water
and wastewater balance. A water balance starts with a process
flow sheet that includes the dynamic variability of flowrates.
Ideally, this balance would include specification limits for
each stream: pressure, temperature, pH and contaminant
Constructing and validating this water balance is not a
trivial task. For a medium-sized refinery, it requires several
hundred hours by a process engineer who is knowledgeable about
the utility water system. Validating the data is especially
difficult because water systems have few flowmeters or
historical flowrate data.
Estimating the requirements for utility water can be
difficult because flowrates may be highly variable due to
seasonal demand. Plant managers should consider temporarily or
permanently installing recording flowmeters to gather data for
a significant period. The information will help to understand
the seasonal and operational variability of water
Tabulate the costs of water and water treatment.
Accurate calculations of unit costs for withdraw, treatment
and charge of water and wastewater will require crafting
defensible economic analyses to justify water reuse projects. Plant and project
personnel must agree on the components for the unit costs. What
set of costs constitute total cost of ownership? Is it a
combination of direct costs and allocated overhead costs or
something else? Some examples include the cost of heat
exchanger cleaning and electrical pumping costs. If you are
forecasting costs for future years, is there a standard
escalation factor included?
Map the water and wastewater streams.
Sometimes, the most cost-effective solution is reuse of a
single wastewater stream within the plant. Consequently, the
proximity of the wastewater stream and the reuse candidate is
important. A map of the water and wastewater flows is essential
to evaluate the feasibility of water reuse recommendations.
Ideally, this map would include additional information about
water and wastewater streams, including equipment (pumps,
storage tanks, sample points) and operating characteristics
(pressures, flowrates and temperatures).
Conduct scenario planning.
Consider all of the alternative water sources such as storm
water and treated wastewater from your facility and/or
neighboring facilities. Ensure that all
contingencies are considered, including increasingly stringent
regulations for effluent quality and restrictions on withdrawal
volumes from the watershed.
Assess the risks to your utility water systems.
Water reuse projects inevitably involve trade-offs between
the expense and complexity of re-treatment and the impact of
modifying the water-quality specification for a proposed
application. Therefore, it is important to understand the
current vulnerabilities of your utility water units. Likewise,
the reuse project should ensure that the
expected changes in water quality do not inadvertently
compromise system reliability or operability under
all anticipated conditions. For example, a reduction
in water quality for a boiler or a cooling tower may result
in higher blowdown (reduction in water and energy efficiency).
It may also reduce heat transfer efficiency due to greater
scaling, thus increasing operating costs for the cooling
Similar to the previous plant efforts to benchmark and to
improve energy efficiency, water reuse will become a strategic
initiative. Water reuse will be an integral part of sustaining
and improving competitiveness in manufacturing. The quality and
availability of water are declining, while the cost for fresh
water is increasing. HP
Loraine A. Huchler is president of
MarTech Systems, Inc., a consulting firm that
provides technical advisory services to manage risk
and optimize energy and water-related systems
including steam, cooling and wastewater in refineries
and petrochemical plants. She
holds a BS degree in chemical engineering, along with
professional engineering licenses in New Jersey and
Maryland, and is a certified management consultant.
She can be reached at