chemical dosing system effectiveness to protect … · chemical dosing system effectiveness to...
TRANSCRIPT
6th European Waste Water Management Conference & Exhibition
www.ewwmconference.com
Organised by Aqua Enviro Technology Transfer
CHEMICAL DOSING SYSTEM EFFECTIVENESS TO PROTECT WATER TREATMENT SYSTEM
Al-Qahtani, N.A.
Saudi Aramco, Saudi Arabia
Abstract
The purpose of this best practice is to provide essential guidelines for automating and
monitoring chemical dosing systems and demonstrate the effectiveness of an automation
system for cooling water system as an example of water treatment system in the industry. This
system results in optimizing chemical consumption eliminating potential hazards.
The performance of costly chemicals changes with time due to operational condition changes.
The chemical optimization activity concentrates on injecting the correct amount of treatment
chemical into a system under the current process conditions, to achieve the result anticipated
from the application of the chemical.
Keywords
Chemical automation, Monitoring system, Cooling water unit, Scale inhibitor, Corrosion
inhibitor, Bio-dispersant.
Introduction
Most treatment chemicals have toxic or other hazardous properties that represent a risk to
human health and the environment. Historically, phosphates, chromates, acids, chlorine and
other biocides have typically been used to treat several applications such as RO water plant,
steam production and cooling tower water. Due to their high toxicity and persistence in the
environment, some of these chemicals, such as chromates, are prohibited from use in cooling
towers. [1]
Several alternative technologies have recently become commercially available to treat any
system used in the industry without the need for chemicals batch preparation. These chemical
treatment technologies claim to have the ability to maintain a product chemistry that prevents
scale and corrosion problems and inhibits adverse bacterial growth in the water treatment
application. [2]
This technology called online chemical automation system plays an important role in the
enhancement of oil and gas processing and production .The automation system consist of ready
mixed chemical with off-the-shelf pumps, sensors and controllers. [3]
6th European Waste Water Management Conference & Exhibition
www.ewwmconference.com
Organised by Aqua Enviro Technology Transfer
Automation system overview
A chemical automation system using online chemical control consists of three main parts as
shown in Figure 1. The first part is the ready mixed chemical container, the second is the control
behavior analyzer subsystem and injection system in the remote site that needs to be
monitored and controlled. [4]
Figure 1: Skid controller with dosage pumps
The ready mixed chemical is provided by manufacturer as an alternative for the existing
chemical that should be prepared by operators. The goal is to eliminate operation intervention
and prevent over or under dosing of the chemicals.
The required fluid flows on a continuous basis through tube into the analyzer unit. The sensors
will analyze how much chemical should be added based primarily on the fluid composition, fluid
chemistry, operating pressure and temperatures, and to some extent the flow regime. The
control device will adjust chemical dosing pumps for the required volume of chemicals.
Most of the operation units have an over capacity chemical dosage pump, which leads to waste
of chemical and power as well. Special pumps with specific capacity are provided with the
automation system for each treatment unit. The required amount of chemical is injected into
the mixed stream through the injection point.
Monitoring System Process
Maintaining the performance and effectiveness of the chemical automation system is extremely
important for key operating parameters control. Program performance is best monitored with
6th European Waste Water Management Conference & Exhibition
www.ewwmconference.com
Organised by Aqua Enviro Technology Transfer
well established key performance indicators (KPIs). To provide quantifiable value, these KPIs
must be jointly developed with the plant for specific system such as water treatment, steam
production, or sour water treatment. [5]
The monitoring program should be installed in the control room to record and monitor all
available operating parameters for the automation system, including flow rates, and chemical
consumption, ensuring that the chemical treatment program is operated and managed
correctly, figure2.
Figure 2: KPI’s for cooling water system as an example
Cooling Water Open Loop Case Study
Process Overview
Industrial cooling towers are to remove the heat absorbed in the circulating cooling water
systems used in power plants, petroleum refineries, petrochemical plants, natural gas
processing plants, and other industrial facilities.
A cooling system consists of a cooling unit (e.g., cooling tower) and a heat exchanger (see Figure
2 below). Cool water is pumped from the cooling tower and circulated through a heat exchanger
to remove heat (i.e., to cool) from hot process fluids. In the heat exchanger, cooling tower water
is warmed as heat is transferred from the hot process fluid to the cooling water. The warmed
water then returns back to the cooling tower. [6]
In the cooling tower, warmed water is sprayed downward, and air is blown upward with a fan.
As the warm water droplets contact the air, some of the water droplets evaporate, and the air
absorbs the heat released from this evaporation thereby lowering the temperature of the
remaining water. An outside source of water, commonly referred to as “makeup water,” adds
more water to the system to make up for evaporation and other water losses. Then the water is
recirculated back to the heat exchanging equipment and the process is repeated. [6]
6th European Waste Water Management Conference & Exhibition
www.ewwmconference.com
Organised by Aqua Enviro Technology Transfer
Figurer 3: Cooling Water open loop process
Chemical injection System
In the cooling water open loop system, various chemicals are used in the treatment of cooling
water; their purpose is to maintain the cooling process in a reliable condition .These batch
chemicals are manually prepared along with manual pump stroke adjustments.
Prior to high chemical consumption along with improper preparation with hazard chemicals; we
at HdGP decided to go with the chemical automation system and this technology has been
implemented for the cooling water open loop, figure 3.
The automation system for the cooling water open loop system is divided into four main parts:
1. Chemical Containers: There are two types of chemicals being used in the system as an
alternative for previous chemicals. In the table below, the alternative chemicals are
being used for the automation system; however, these chemicals are already mixed
with additives and prepared in special containers to be installed in the process area.
Table 1: Alternative chemicals used in cooling water open loop system.
Manufacture Product Function Location
Phosphate
Scale/Corrosion
Inhibitors
A highly effective phosphonate based scale and
corrosion inhibitor developed for the treatment of
cooling water systems. Upstream of
tower basin
Bio-dispersant
A non-ionic surfactant/dispersant for removing
and dispersing microbiological slime deposits.
6th European Waste Water Management Conference & Exhibition
www.ewwmconference.com
Organised by Aqua Enviro Technology Transfer
2. Sized Chemical Pumps: The chemical pumps are sized based on the treatment system
demand and type of chemicals being utilized.
3. Control Analyzer: To detects the upsets that precede scaling, corrosion and biofouling
and then delivers the appropriate chemical response.
4. Sample and Injection Points: The sample point is located in the outlet header of the
cooling water basin, whereas the injection point is set up on the return header into the
cooling water tower, which is the most effective position for injection.
Automation Result
Over the first several months of operation after the automation chemical program was
administered, a clear stable in the data trend and chemical concentration for the permeate
quality was noticed, figure 4.The figure shows how automation affects the performance of
treating cooling water by chemicals .In figure 4, the phosphate concentration was not stable,
which was sometimes below or above the permissible range, whereas the concentration after
automated scale inhibitor dosing is within the limit range as well as corrosion inhibitor in
figure 5.
Figurer 4: Phosphate concentration behavior before and after automation
6th European Waste Water Management Conference & Exhibition
www.ewwmconference.com
Organised by Aqua Enviro Technology Transfer
Figure 5: Corrosion concentration behavior before and after automation
This automation results in stability for water chemistry and therefore does not have the huge
fluctuations that occur when a lot of bathers enter a spa. In addition, it minimizes or may even
eliminate damage to the equipment itself. Particularly in the case of heaters, such as heat
exchangers, large fluctuations in sanitizer level or pH will act upon and corrode the heat
exchanger itself. By keeping the levels steady, scale, erosion and corrosion are minimized;
thereby extending the life of the equipment. The constant monitoring and adjusting
accomplished by a chemical automation system takes care of the water chemistry product.
HdGP is not using as much of the dosing chemicals because the water quality has not been
combating the huge fluctuations. As a rule of thumb, a chemical automation system can pay for
itself within approximately a two year period of time.
Conclusions
This innovative technology is a comprehensive system to enhance and optimize the
performance of any treatment program. It is a completely integrated solution for accurate
dosing along with an associated performance monitoring system and troubleshooting advice.
The automation enables “service on demand,” avoiding unnecessary operation intervention
with chemical batch preparation along with eliminating dosing unnecessary variation chemicals,
which affects environment conditions.
The experience shows that after applying online chemical control technology for RO water
treatment and cooling water systems. There is a clear reduction in operating costs. In addition,
the equipment life was extended while minimizing environmental impact, improving employee
safety, and conserving high quality resources for human consumption or industry process.
The online chemical control technology is not limited for only water treatment units, but it can
also be applicable for other applications in the gas and oil industry such as a condensate
stabilizer unit and gas processing unit. Finally, it is recommended to apply the same
methodology for the existing chemical treatments in both gas and oil facilities.
Acknowledgements
I would like to acknowledge and extend my heartfelt gratitude to the following persons who
have made the completion of this paper possible:
Our Manager, Mr. Abdullah B. Al-awadh, for his vital encouragement.
Our operation superintendent, Mr. Abdullah A. Al-Amir, who is the owner of this grateful idea,
for his follow up and support.
Our engineering superintendent, Mr. Mohammed Y. Al-Rashid, for his understanding and
assistance. Mr. Khalid S. Swoluem , Supervisor, Process Engineering unit.
6th European Waste Water Management Conference & Exhibition
www.ewwmconference.com
Organised by Aqua Enviro Technology Transfer
Mr. Abdulaziz S. Al-Kamas for the help and inspiration he extended.
All operation and process engineers faculty members and Staff
References
Baruth, Edward E., ed. “Water Treatment Plant Design,” 4th Edition. New York: McGraw-Hill,
1990.
Kawamura, Susumu. “Integrated Design and Operation of Water Treatment Facilities,” 2nd
Edition. New York: Wiley, pp. 74-5,2000.
Willmon, J.G. and Edwards, M.A. “Pre commissioning to Startup: Getting Chemical Injection
Right,”.SPE 96144, SPE Annual Technical Conference and Exhibition, Dallas, Texas, 9 – 12
October 2005.
W. C. Fortt, E. S. Berm, R. C. Strong and Ma. Vegesi" Process Design of Injection Systems,"
Corrosion 96, NACE International, Paper No. 587, 1996.
Al-Qahtani,Nasser A. “Chemical automation system,” Saudi Aramco best practic ,Juanuary 2012.
NACE RP0300-2000 “Pilot Scale Evaluation of Corrosion and Scale Control Additives for Open
Recirculating Cooling Water Systems”. National Association of Corrosion Engineers, 16-Jun-2000.