ENVIROMENTAL MAINSTREAMING TOOL (EMT) : APCS

GENERAL PROCESS DESCRIPTION

Scrubber systems are a diverse group of air pollution control equipment that can be used to remove contaminants from industrial exhaust streams. LEE RUBBER CO. (PTE),. LTD , KUALA KANGSAR BRANCH (SMR Factory) adopts the Packed Tower Wet Scrubber as their air pollution control devices. In wet scrubber system, scrubber can be designed to collect particulate matter and/or gaseous pollutants. Typically wet scrubber remove dust particles by capturing them in liquid droplets. While the gaseous pollutants, wet scrubbers remove them by dissolving or absorbing them into the liquid. The good scrubber design must provide maximum contact between liquid and dirty gaseous.

INTRODUCTION OF WET SCRUBBER

Wet scrubber is basically a variety of devices that use liquid to removed pollutants.

In a wet scrubber, the dirty gas stream is brought into contact with the scrubbing liquid by spraying it with the liquid, by forcing it through a pool of liquid or by some other contact method.

The design of any air pollution control device depends on the industrial process and the nature of the air pollutants involved. Exhaust gas characteristics and dust properties, if particles are present, are of primary importance. Scrubbers can be designed to collect particulates and/or gaseous pollutants. Wet scrubber remove particles by capturing them in liquid droplets. Wet scrubbers removed pollutants gases by dissolving or absorbing them into the liquid. Any droplets that are in the flue gas then be separated from the clean exhaust stream by means of another device referred to as a mist eliminator. Also, the resultant scrubbing liquid must be treated prior to any ultimate discharge or reused in the plant.

There are numerous configurations of scrubbers and scrubbing systems- all designed to provide good contact between the liquid and dirty gas stream.

Figure 1.0 shows an example of wet scrubber adopts at LEE RUBBER CO. (PTE),. LTD , KUALA KANGSAR BRANCH (SMR Factory)

CONSTRUCTION OF VERTICAL PACKED TOWER SCRUBBER

A basic packed tower unit is comprised of a column shell, mist-eliminator, liquid distributors, packing materials, packing support and may include a packing restrainer. Corrosion resistant alloys, steels or fiber are required when highly corrosive solvents or gases are used. Ducts are required to transport exhaust gas while gas while pumps, nozzles and pipes transport liquid to and from the scrubbing vessel.

The shell is sometimes lined with a protective membrane, often made from a corrosion resistant polymer. For absorption involving acid gases, an interior layer of acid resistant brick provides additional chemical and temperature resistance.

At the packed section, packing materials provide a large wetted surface for the gas stream maximizing the area available for mass transfer. Packing life varies depending on the application.

A liquid distributor is designed to wet the packing bed evenly and initiate uniform contact between the liquid and vapor. The liquid distributor must spread the liquid uniformly, resist plugging and fouling, provide free space for gas flow and allow operating flexibility.

At high gas velocities, the gas exiting the top of the column may carry off droplets of liquid as a mist. To prevent this, a mist eliminator in the form of corrugated sheets or a layer of mesh can be installed at the top of the column to collect the liquid droplets, which coalesce and fall back into the column.

Figure 1: Schematic Scrubber.

MEASUREMENT BEFORE START-UP

1. Check List Before Start-Up

Equipment		Remarks
Utilities	Incoming power supply	Verify proper power to control panel/components
	Incoming water supply	Verify proper water supply connection
	Waste water discharge	Verify overflow & drain properly
Mist Eliminator	Installation	Inspect mist eliminator for proper installation
Packing	Installation	Verify packing height installation
Nozzles	Installation	Verify spray nozzle installation & tightened
Pumps	Pump rotation	Verify correct rotation of pump
	Installation	Check for leaks, vibration &unusual noise
	Lubrication	Verify pump grease prior to start-up
	Discharge pressure gauge	Verify water pressure gauge properly installed & operation
	Electrical interlock	Verify proper wiring connection to motor
Piping	Installation	Verify piping & valve connection are tightened
Piping	Water flow meter	Verify wfm properly installed & operational
Fan	Installation and rotation	Check for vibration and verify correct rotation
	Pulley, shaft & belt	Safe guard need to be provided
	Inspection door	Closed
Other	Ducting, inlet & outlet	Check to ensure no obstruction
	All inspection manholes	Close air tightly
	Lubrication	Verify fan motor & bearing lubrication prior to start –up
	All other mechanical parts (eg ducting joints)	Ensure they are all securely fasten.

MEASUREMENT DURING START-UP

2. Check list during Start –up

No	Procedures
1	Open the water supply valve and check for leaks. Ensure that the wastewater drains is connected.
2	Fill scrubber sump or remote tank with freshwater until water begins to overflow
3	Start pump
4	Start fan
5	Immediately check stack discharge. If excessive misting is observed shut system down immediately and consult factory.
6	Check to see that water flow is set to required value. Water flows below this rate cause pollutant escape in the scrubber exhaust line
7	Check the pressure gauge and the pressure drop should be monitored across specific scrubber components.
8	The pH of the scrubbing liquid feeds streams and/or recycle liquor systems should be monitored.
9.	The unit should operate quietly and vibration free. The bearings and shaft should be warm to the touch.
10.	Walk one round to ensure the system is safe for operation to avoid any injuries.

MEASUREMENT FOR SHUT DOWN

3. Check List For Shut Down

No.	Procedure
1	Switch off the fan and isolate the scrubbing system from operation
2	Allow the recirculation liquid system to continue for 20 min
3	Purge scrubber for 10 minutes
4	Turn off purge gas
5	Close valve between scrubber and central exhaust.
6	Turn off the scrubber power
7	Turn off water
8	Disconnect power before control box is opened.

CURRENT ‘PERFORMANCE MONITORING PROCEDURE

A procedure was made to ensure each typical form will be recorded accordingly, such as pre-start up inspection, routine start-up and routine shutdown.

From all data from performance monitoring record, we can determine which areas need to do the maintenance work. For example, clogged at demister or packing can be identified by pressure drop reading. All document related to scrubber will be kept properly.

Refer Appendix I for TYPICAL FORM TO RECORD PERFORMANCE DATA / ACTIVITIES OF SCRUBBER

Troubleshooting is important in operating a scrubbing system. So, the committees of Malodour Treatment Plan also immediately carried out troubleshoot if any abnormality detected. During shutdown, major maintenance was scheduled to ensure cleaning at packing material, demister etc. can be made and physical inspection of scrubber condition i.e. housing and ductwork can be carried out.

A current report will be presented by the committee once a year to update the top management for review and revision of performance monitoring requirements.