CHEMICAL DOSING SYSTEM EFFECTIVENESS TO PROTECT … · CHEMICAL DOSING SYSTEM EFFECTIVENESS TO PROTECT WATER TREATMENT SYSTEM Al-Qahtani, N.A. Saudi Aramco, Saudi Arabia ... the equipment

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]

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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





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]





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.





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





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.





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.


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CHEMICAL DOSING SYSTEM EFFECTIVENESS TO PROTECT … · CHEMICAL DOSING SYSTEM EFFECTIVENESS TO PROTECT WATER TREATMENT SYSTEM Al-Qahtani, N.A. Saudi Aramco, Saudi Arabia ... the equipment