CHEVRON - Chemical Injection System Design

ystem ider-

e

2500 Chemical Injection System Design

AbstractThis section discusses the process control and design of a chemical injection sfor a cooling tower. Included are discussions of automatic controls; design consations; types of containers for feeders and storage; location of facilities; chlorininjection facilities, with sizing, piping, and location; system commissioning; and safety requirements.

Contents Page

2510 Process Control 2500-2

2520 Automatic Controls 2500-2

2521 Instrumentation

2522 Packaged Controls

2530 Chemical Injection System Design 2500-3

2531 Introduction

2532 Chemical Entry

2533 Design Considerations

2540 Chlorine Injection Facilities 2500-6

2541 Introduction

2542 Nature of Chlorine

2543 Design and Process Considerations

2544 System Commissioning

Chevron Corporation 2500-1 December 1989

2500 Chemical Injection System Design Heat Exchanger and Cooling Tower Manual

ss

trol

ting ters

ny

are

2510 Process ControlFigure 2500-1 shows the common components of a typical cooling tower procecontrol scheme. The mechanisms of corrosion and fouling and how they are controlled are discussed in Section 2400. Consult the ETD Monitoring and ConSystems Division for help in this area.

2520 Automatic Controls

2521 InstrumentationAutomatic units ensure control of critical variables at the optimum values, resulin an efficient system at a minimum operating cost. Close regulation of parameis also important for minimizing waste disposal. Many practical features can bebuilt into the instrumentation to achieve maximum dependability. Such featuresinclude:

1. Sensing units located at the cooling tower to minimize response time.

2. Preamplification of the signal at the sensing point so it can be transmitted adistance without interference.

3. Instruments located in the control room or other locations where personnelavailable.

Fig. 2500-1 Typical Cooling Tower Process Control

December 1989 2500-2 Chevron Corporation

Heat Exchanger and Cooling Tower Manual 2500 Chemical Injection System Design

, an

ten-

d

low-

er-ti-

ical

y , anti-

te-s

he

4. Dependable, solid-state electronic recorders to observe trends.

Generally, an automatic system provides a package to measure and control theinhibitor level (chromate or nonchromate), conductivity for blowdown control, pHand, in many cases, corrosivity. The corrosivity device serves as a backup or asoverride on the system to provide an alarm or perform certain functions that areprogrammed in for rapid restoration of normal conditions.

Chlorination programs can be automated by using ORP (oxidation reduction potial) instruments. Liquid nonoxidizing biocides are frequently injected into the cooling system automatically by timing devices which operate proportioning feepumps.

2522 Packaged ControlsBoth Uni-Loc and Magna Corporation offer packaged control systems for pH, bdown, and inhibitor addition. Controls should be designed so that they may be expanded to use the various control options available. As environmental considations restrict, and probably eliminate, the discharge of chromates, more sophiscated cooling tower controls will be needed.

2530 Chemical Injection System Design

2531 IntroductionThis section discusses the design, equipment selection, and installation of cheminjection facilities for additives injected from:

• Drums• Semibulk portable containers• Bulk storage tanks

The discussion applies to facilities used for purchased-outside products typicallintended as additives to process plant streams, such as antifoulants, antifoamsoxidants, corrosion inhibitors, boiler feed water additives, acids, caustics and cooling tower additives.

2532 Chemical EntryWe are legally required in many locations to document and provide specific marial hazard information for all personnel who might be exposed to the hazardoumaterials. These requirements include:

• Reviewing and approving all chemicals which are used in a plant

• Posting the identity of the material and the appropriate hazard warning on tcontainer

• Providing a Material Safety Data Sheet before the material is used



s s for

d s Full

ir h as

, ease ts,

anks

vessel he sels ed

at-). , or

the its

s.

The engineer is responsible for verifying that all of the local rules and regulationhave been complied with. Consult the local safety and environmental specialistthe most up-to-date rules and regulations.

2533 Design ConsiderationsRichmond Refinery Drawings D-253080, B-603003, and B-603005 are StandarP&IDs for bulk, semibulk, and barrel chemical injection facilities. These drawingare attached at the end of this section as Figures 2500-2, 2500-3, and 2500-4. size prints and CAD files are available from the Richmond Refinery Drafting Department.

Note that the attached P&IDs were generated at the Richmond Refinery for theProcess Hazard Safety Committee. Consequently, some of the information, sucreferences to refinery instructions, is specific to Richmond.

Types of ContainersThe choice of containers for feeding chemicals, such as acid, caustic, inhibitor,dispersant, biocide, etc., depends on the type of controls, the desired inventoryof replenishing stock, handling problems, cost of chemicals in bulk and drum loand, most importantly, the safety and environmental considerations involved.

Bulk Storage Tanks (see Figure 2500-2 drawing D-253080)For large quantities and where tank truck deliveries are required, bulk storage tare the best option. Often vendors will supply the tank; however, the tank must sometimes be upgraded to meet local standards.

Steel storage tanks should be designed to UL-142 or equal (unless a pressure is required, then use ASME Code, Section VIII, Division 1). All connections to tvessel must be 3/4-inch minimum size and must be seal-welded or flanged. Vescontaining flammable material require a bottom fill nozzle and a vent system sizfor emergency venting (per NFPA 30 and API STD-2000).

High-density polyethylene (HDPE) storage tanks may be used if they are compible with the material stored (HDPE should not be used to contain combustiblesHDPE tanks should be designed to Poly Cal Plastics’ specification PCPP48614equal, for cross-linked polyolefin tanks.

Semibulk, Portable Returnable Container (see Figure 2500-3 drawing B-603003)Semibulk containers offer the advantages of returnable containers supplied by vendor and are easily handled by a forklift or crane. Skid-mounted standard unwith attached pumps offer great convenience at low first cost and eliminate or reduce capital expenditures. Material unit cost is usually cheaper than for drumHowever, not all vendors offer this option. Note that some upgrade of vendor-proposed piping and equipment is usually required to meet local standards.



d ter-aste

the he d ).

e still e n n.

uty

r n on

O.D.,

.

e r

Drums (see Figure 2500-4 drawing B-603005-0)Use of drums should be avoided unless the quantity to be used is very small anreturnable, or bulk facilities cannot be justified. Drums may be an acceptable alnate, however, for temporary uses (test runs). Drums are costly to dispose of, wchemicals because they do not empty completely, and may result in higher employee exposure. Drum handling is difficult and can cause injuries.

Location of FacilitiesThe facilities should be located in an easily accessible area, preferably around perimeter of the plant. Give consideration to the access of the truck delivering tbulk shipment, ease of operator access on normal rounds, and to the nature anpotential hazard of the material (i.e., decomposition of the material if near a fire

Injection PumpsThe injection pump(s) should be located as close as possible to the vessel whilmaintaining the proper clearances. For bulk storage facilities, if possible, elevatthe pump(s) approximately 3 feet for ease of operation and maintenance. MiltoRoy, Pulsafeeder, or Williams pumps may be used, depending on the applicatio

InstrumentationA combination level gage/rate meter is allowable; however, it should be heavy dto avoid spills resulting from mechanical damage. The suggested model is a KENCO calibration gage (or equal). Since each facility’s pump flow rate is different, the KENCO model number must be obtained from the vendor.

PipingConsider seal welded or socket welded piping 3/4-inch minimum. The type of chemical may require a material other than steel. The ETD Materials Division othe material vendor should be consulted. Some injection quill designs are showthe referenced P&ID. To facilitate pump hookup or to decrease costs in long discharge runs, stainless steel tubing (or another alloy) is acceptable (1/2-inch 0.065-inch minimum wall).

LightingProvide adequate lighting for the operating and maintenance activities requiredConsult the local safety engineer for the level of lighting required.

BermsThe decision to berm the facilities should be based on the volume, and on the impact on the effluent treatment system in the event of a spill. The intent is to contain any spills to a confined area and to keep the material out of the drainagsystem. Berms should be large enough to hold all contents of the largest tank incase of rupture and should contain any slight spillage from the loading spot andfrom taking the facilities out of service for maintenance. A 2-inch minimum gatevalve (normally closed) should be provided in the berm, through which rainwate



tial

rds, ssed

cter-eavy

ost ver e the

gas

lty of ver

ntact ddi-

can be drained from the bermed area. Adequate washdown facilities should beprovided near the facilities.

Safety RequirementsEach facility must be evaluated to determine if the following safety equipment isneeded:

• Safety showers and eyewash stations a minimum of 10 feet from any potenleak source and a maximum of 50 feet (unobstructed) from the facility for corrosive chemicals

• Safety signs

• Barriers or guard posts around the perimeter per Standard Drawing GA-S99975 (located in the Civil and Structural Manual)

• Scott Air-Pak

• Posting of instructions for the driver of the bulk delivery truck

2540 Chlorine Injection Facilities

2541 IntroductionThis section gives guidance on the design of cooling tower chlorine injection systems. In order to complete a detailed design, you must understand the hazaregulations, and safe handling guidelines for chlorine. These subjects are discuin detail in the Piping Manual, Section 1500, and in general terms in this section.

2542 Nature of ChlorineChlorine is a nonflammable gas which is liquified under pressure. It will react chemically (often vigorously) with almost all elements and with many inorganic and organic substances, usually with the evolution of heat. The gas has a charaistic odor and a greenish-yellow color, and is about two and one-half times as has air. Thus, if it escapes from a container, it will seek the lowest level in the building or area where the leak occurs. Although dry chlorine will not corrode mmetals, it is very corrosive (forms HCl) when moisture is present. Therefore, neuse water on a chlorine leak because resulting corrosive conditions always makleak worse.

There are potential health hazards associated with the use of chlorine. Chlorineis primarily a respiratory irritant. In sufficient concentration the gas irritates mucous membranes, respiratory system, and skin. In extreme cases, the difficubreathing may increase to the point where death can occur from suffocation. Neattempt a rescue without adequate respiratory protection. Liquid chlorine, in cowith skin or eyes, will cause burns. Consult the Material Safety Data Sheet for ational information.



s n

g e

und

about

or

warm

di-ase.

er

era- the

w

or

e

2543 Design and Process ConsiderationsThe primary use for chlorine is for cooling water treatment. Chlorination reducethe growth of algae and fungi which, left untreated, can cause severe depositioproblems and cell attack on metals.

Chlorine normally comes in 150-pound or 1-ton containers. Drawings D-603001and D-603002 are standardized P&IDs that can be used as a basis for designinchlorine facilities for cooling water treatment. These drawings are attached at thend of this section as Figures 2500-5 and 2500-6. Full-size prints and CAD filescan be obtained from the Richmond Refinery Drafting Department.

Sizing of the FacilitiesThe dependable continuous discharge rate of chlorine gas from a single 100-poor 150-pound cylinder without frosting under normal conditions (70°F) is about 1.75 pound/hr against a 35 psi back pressure. The rate for a 1-ton container is 15 pound/hr under similar conditions.

If the gas discharge rate from a single container will not meet requirements, twomore can be connected to a manifold and discharged simultaneously, but all containers should be at the same temperature to prevent transfer of gas from acontainer to a cool container. If a container becomes completely filled with liquidand the container valve is then closed, the container may burst from hydrostaticpressure.

Minimize the number of chlorine cylinders that are hooked up to the system. Adtional cylinders and associated piping increase the risk of having a chlorine releNormally a 4-week supply should be adequate.

Where to Inject ChlorineChlorine should be injected into the tower basin on the opposite side of the towfrom the forebay to maintain a sterile condition in the tower basin. If chlorine is added to the forebay, it will not reach the basin because it evaporates through ation as the water cascades down over the tower fill. In order to efficiently sweepbasin, a chlorine distributor that extends the full length or width of the basin is normally employed. This distributor should be located approximately 2 feet belothe basin water level.

PipingPiping arrangements should be as simple as possible. Joints should be flangedwelded with the number of flanged joints held to a minimum. Piping systems should be well-supported and adequately sloped to allow drainage; low spots should be avoided.

Construction materials and ratings for Monel pipe are shown on the attached P&IDs for cooling water chlorination facilities. The cylinders are connected to thpiping system by a Chlorine Institute transfer hose. A pressure-reducing valve should be installed between the cylinder and the regulator.



mper-ne

pair

ator id

uid

to be

mit

sole-sary

n

r ine

ored

r ine

Piping Expansion and ProtectionSuitable allowance should be provided for pipe expansion due to changes in teature. Liquid chlorine has a high coefficient of thermal expansion. If liquid chlori(containing no gas bubbles) is trapped between two valves, high pressure will develop with an increase in the temperature of the chlorine and a rupture couldoccur. For this reason the standard designs shown on the P&IDs have only oneof isolation valves (one main plus backup).

Preventing Liquid to the ChlorinatorNo liquid chlorine can enter the chlorinator, as this usually damages the chlorincomponents. The following methods can be used to reduce the chances of liquchlorine entering the chlorinator:

• Install a pressure reducer (as shown on the P&IDs) to flash any residual liq

• Have a 120 volt heater installed in the chlorinator (most can come factory-equipped)

• Install a liquid trap in the piping just upstream of the chlorinator

Chlorinator DesignChlorinators are usually sized to provide 1 ppm of chlorine continuously to the circulating water. For example, for a system with a circulation rate of 13,000 gallons per minute (156 million pounds per day) the chlorinator should be sizeddeliver approximately 156 pounds per 24 hours. A margin of 20 to 25% should added to the chlorinator design capacity.

Chlorinators are typically automated by equipping them with timers that permit either a daily or several times weekly application. These timers should also percomplete flexibility for the length of each application. However, the typical dura-tion is somewhere between 2 and 8 hours. The timer is usually connected to a noid valve on the water supply to the chlorinator. Since a flow of water is necesto operate a chlorinator, interrupting this flow with a suitable automatic, full-opening valve provides a simple and reliable method of turning the equipment oand off.

Vacuum EductorThe chlorinator is actuated by an inducted vacuum from an eductor. The eductouses the flow of water to pull a slight vacuum on the chlorine system. The chlorflow can be controlled by a variable rate rotameter.

Where to Locate Chlorine ContainersExposure of containers to flame, intense radiation heat, or steam lines must beavoided. If the fusible plug reaches 158°F the plug will melt and chlorine will escape to the atmosphere. For cooling water treatment, the cylinders can be stoutdoors but they should be located at least 50 feet from the tower or from any other flammable materials. If they must be located closer than this, a building ofire wall should be designed and constructed to protect all elements of the chlor



nd

ate--

hlo-

e is is

n ine

tested.

system from fire hazards. Positive hold-down clamps should be provided for allchlorine containers.

Miscellaneous Safety EquipmentThe chlorine facilities should be well lighted and identified by “Cl2 Hazard” and “No Parking” signs around the perimeter. Barriers of guard posts should also beinstalled around the perimeter. An eyewash, Scott Air-Pak, protective clothing, ashower should be located within 50 feet of the chlorine.

2544 System Commissioning

Cleanup After FabricationIt is especially important to clean all portions of a chlorine system before use because chlorine may react violently with cutting oil, grease, or other foreign mrials. Cleaning may be accomplished by pulling a cloth saturated with trichlorethylene (or other suitable chlorinated solvent) through each length of pipe. Chlorinated solvents can produce serious physiological effects if not used in strictest compliance with the solvent manufacturer’s safety recommendations. Never use hydrocarbons or alcohols because residual solvent may react with crine.

Pressure TestingAfter hydrostatic testing, the piping must be dried. This can be done by passingsteam through the lines from the high end until the lines are thoroughly heated.While steaming, allow condensate and foreign matter to drain out. While the linstill warm, nitrogen (or dry air) should be blown through the line until it is dry; thmay require several hours.

After drying, the system should be pressurized to 150 psi with dry air or nitrogeand tested for leaks by application of soapy water to the outside of joints. Chlorgas may then be introduced gradually and the system tested for leaks. Never attempt to repair leaks by welding until all chlorine has been purged from the system. When all detectable leaks have been repaired, the system should be re


2500 Heat Exchanger and Cooling Tower Manual

December 1989

Heat Exchanger and Cooling Tower Manual

Chevron Corporation 2500-11

Fig. 2500-2 Engineering Drawing D-253080-0


December 1989



Fig. 2500-3 Engineering Drawing B-603003-0


December 1989



Fig. 2500-4 Engineering Drawing B-603005-0


December 1989



Fig. 2500-5 Engineering Drawing D-603001-0


December 1989



Fig. 2500-6 Engineering Drawing D-603002

CHEVRON - Chemical Injection System Design

Documents

cooling tower manual

meet local standards

cooling water treatment

bulk storage tanks

cooling tower

tower basin

normal conditions

guard posts