When planning or designing an odor control system one should pay close attention to several key variables that can cause havoc on a chemical odor control scrubber when trying to treat hydrogen sulfide or ammonia gases. The need for odor control occurs for many different forms and it is important to have a good understanding of the process that is creating the odorous or corrosive gas and the need for the odor control & air emissions treatment.
First begin to identify
all the potential obstacles that may creep up later after the chemical odor or corrosive gas control system goes on line like acid or caustic consumption. As an example, chemical odor control systems that are designed for water treatment for the municipal industry are typically needed and attached to a degasfication or decarbonation process which are often needed to treat hydrogen sulfide (H2S). However, many times designers may not pay close enough attention to the type of water process that is available to use for “make-up” water for the chemical scrubber and with the addition of caustic this can create scaling or fouling. This unknown variable of the make up water quality can lead to a complete tower shutdown if the chemical scrubber distribution and media bed scales or fouls. The most commonly used chemicals for a hydrogen sulfide (H2S) scrubber are either chlorine in the form of sodium hypochlorite or caustic in the form of caustic soda. Both of these chemicals are both common to a water treatment facility and already in place for the adjustment and control of pH.The makeup water plays a significant role
in the operation of a chemical scrubber and when water containing to high levels of hardness levels is used as the source for the makeup water your chemical scrubber can become fouled and scaling can occur in a matter of hours depending on the alkalinity and salts within the water. Solidification can occur from the scaling when combining sodium hypochlorite and raw feed water at certain pH ranges and these ranges are normally the range needed to achieve peak performance. Calcium chloride will form and your chemical odor control scrubber and will become a solid chunk of calcium chlorite making the ability for water or air to pass freely through the media packing next to impossible. No matter what type of media packing is utilized in the odor control or gas scrubber it can foul and scale if the water chemistry is incorrect. Trust me when I say “been there and done that” ! I have seen operators who have allowed a chemical scrubber to become out of balance with pH control and completely solidify the tower column to the degree that neither air nor water passage is possible. With ammonia scrubbers the problem can still occur but are different with different sets of parameters.
The best way to keep your chemical scrubber operating
at an optimum level is to make sure the makeup water is free from hardness (salts) and the alkalinity is corrected through pH adjustment with acid and caustic injection. I recommend either using permeate water from a reverse osmosis system or adding a softener to condition the water prior to it entering the chemical scrubber. Next, always maintain your pH monitoring and feed control systems because if they become unreliable then your chemical scrubber can be headed to certain disaster if the caustic, acid, or hyper-chlorite feed system fails and of course your removal efficiency will drop. Many times, operators will just increase the chlorine feed system to the point where they smell only chlorine leaving the tower and assume that the tower is operating effectively. But the reality is that the scrubber may only be treating 80% of the hydrogen sulfide (H2S) gas and the balance is being masked by the chlorine smell. Some may ask why this is not a good practice to adapt? Soon with the new technology being deployed by DeLoach Industries the different types of chemical scrubbers for off gas treatment and hydrogen sulfide treatment may be able to correct themselves with minimum operator interactions. DeLoach Industries is quickly adapting “aritifical intelligence” (AI) into their line of chemical odor control, biological odor control, degasficiation, and decarbonation equipment systems. The answer is that the excess chlorine gas is not only expensive it is dangerous to humans and to corrosive to all surrounding equipment. The equipment in and around a chemical scrubber will begin to immediately corrode and electronics can fail quickly with the aggressive corrosion brought on by the excess chlorine gas that can be released when the scrubber is not operating in an optimal manner.
It is always best to operate the chemical scrubber
in the method it was designed and within the parameters recommended by the manufacturer. Make sure you monitor the makeup feed water and the pH of the recirculating water and add caustic or acid as needed. Keep a watchful eye on the water and always check the Langelier Saturation Index number and remember that if it is out of balance it can create havoc to the chemical odor control treatment system and adjustment to your caustic or acid feed system may be needed or in a matter of hours or over a short duration of time. When treating ammonia gases the chemical reagents are different but the need to control the pH remains the same. The addition of caustic is always needed when stripping ammonia from a water stream process and the pH must remain high to remove the ammonia from the water and release it as a gas to treat in a scrubber. If the LSI number is too much in the positive you will create the perfect situation for scaling. remember, the most common form of scaling in a chlorine and caustic odor control system is calcium carbonate and once fouled it can be quite difficult to reverse the process. Always check with the system manufacturer.
At DeLoach Industries we receive calls from operators who have misplaced the O&M manual or just want to be sure who are rightfully looking for the correct operating parameters to keep the chemical scrubber performing at the design levels. We always provide immediate assistance to operators who we know and recognize are trying to keep our systems and their water treatment plant running in top performance. If you need further assistance with an odor control scrubber the professionals here at DeLoach Industries, Inc will be happy to assist you (941) 371-4995.