Controlling TRS Emissions with Oxygen Versus Peroxide – an evaluation
At a glance
Pulp and paper mills total reduced sulfur compounds (TRS) emissions face many challenges to remain compliant with federal and local regulations. Each emissions solution is met with necessary CAPEX vs. OPEX cost evaluation. Since each case is unique, an evaluation is recommended to determine the best approach.
There are two common ways to control TRS emissions, by adding oxygen or hydrogen peroxide to the effluent prior to entering the treatment units. There are advantages and disadvantages to each. Effluent from pulp and paper mills often contain several hundreds of parts per million of sulfate as well as 0.1 to 10 parts per million of TRS. This can result in nuisance hydrogen sulfide emissions from non-aerated primary treatment units, e.g., pre-settling basins or clarifiers. Both chemicals react very quickly and have been shown to be effective.
For example, a Kraft mill is treating 20 million gallons per day of effluent in a primary clarifier. Oxygen can be added to suppress sulfate reducing bacteria and oxidize the bisulfide. Another approach would be to add hydrogen peroxide. Hydrogen peroxide oxidizes the TRS compounds and is a relatively mild disinfectant.
There are several ways to inject oxygen including the following most common:
- Direct injection into a full inlet pipe with sufficient residence time
- Side-stream injection and injection of supersaturated effluent into the inlet pipe
Under proper conditions the direct injection method can transfer 50% of the oxygen applied. Side-stream system can achieve 75% – 95% efficiency. For this case, our assumption is a BlueInGreen side-stream system with a design capacity of 5,000 pounds per day and a utilization rate of 2,500 lbs/d. For this example, the installed cost of the oxygen system would be approximately $2,200,000.
A hydrogen peroxide system would be much less expensive to install. The expected installed cost of the peroxide system would be $150,000. However, the chemical costs would be many times higher. For this case, we are assuming an average of 500 gallons per day of 34% hydrogen peroxide would be required.
To demonstrate this case, we are using the following operations & maintenance costs:
| Oxygen Injection | Installation Cost | Annual Cost |
|---|---|---|
| 2 Units | $2,200,000 | |
| Oxygen Costs* | $45,625 | |
| Lease of Oxygen, vaporizers, etc.* | $48,000 | |
| Electrical costs | $68,312 | |
| Maintenance | $115,061 | |
| Labor | $32,500 | |
| Total O&M costs/year | $309,498 | |
*The expected O2 cost would be $125 per day. Lease of an O2 storage tank, vaporizer and control equipment would be $4,000 per month. |
||
| Peroxide Injection | Installation Cost | Annual Cost |
| 1 unit | $150,000 | |
| Peroxide cost** | $974,550 | |
| Electrical costs | $20,494 | |
| Maintenance | $12,000 | |
| Labor | $16,250 | |
| Total O&M costs/year | $1,023,294 | |
** Most of this cost is the chemical cost of $2,700 per day. |
||
Installation cost annual cost
There are other advantages to using either system:
Oxygen injection does not react with primary solids, e.g., fiber fragments. High intermittent losses of fiber stock can interfere with the peroxide dosing.
Peroxide has the potential for oxidizing other odorous compounds, e.g., methyl mercaptan. A disadvantage, it can react with non-odorous compounds and at higher dosages generate biochemical oxygen demand by partially treating recalcitrant organics.
Based on this analysis, if your project is expected to last more than three years, oxygen is the best option. If the project is less than three years, peroxide is the better option. While each project is different, looking at the CAPEX and OPEX is a critical step to choosing what is right for you and your project.