05/03/2021 | Agriculture and Farming | 8 MINUTE READ

Managing a Boiler Blowdown Control System

Whether you work in a food processing plant or manufacturing facility, it’s likely that you use a boiler in your day-to-day operations. Boilers work by heating water until the water evaporates into steam. When you use a boiler in your facility, it’s important to understand that the system must be well-maintained if you want it to operate at peak efficiency. Over time, the number of dissolved solids in your boiler water will increase until scale develops.

Scale is a kind of hardened deposit that can develop on surfaces along with the boiler. When this occurs, your boiler will become less efficient. If not quickly corrected, an entire system malfunction may occur, which might result in the boiler needing to be replaced. In order to mitigate this issue and keep your boiler in good working condition, it’s highly recommended that you perform the boiler blowdown process, which occurs by removing water from your steam boiler while the boiler itself is in operation.

Completing this process allows you to effectively remove the suspended solids in the water as well as any sludge at the bottom of the system. By removing suspended solids on a regular basis, you can be confident that your boiler will generate clean steam. Keep in mind that this process will also prevent the surface of the water from foaming, which heightens the possibility that water levels become unstable.

When the blowdown water is removed from the boiler, it must be at the exact pressure and temperature that the boiler is currently operating at. Once this water has been discharged to a drain, some of it will flash into steam, which helps to reduce the temperature of the water to where it needs to be. The water that’s removed from the boiler will be replaced with fresh feed water.

If you want to correctly perform the blowdown process, it’s important to understand that the blowdown rate must be exact. In order to rapidly remove as many contaminants as possible, the blowdown rate should be high. The factors that determine what the blowdown rate should be for your boiler include the operating conditions, the design of the boiler, and the contaminant levels of the feed water. This article provides you with a complete rundown of how to manage the blowdown process for your boiler.

Two Sources of Blowdown Water

boiler water systemThere are two separate methods that you can use to complete the boiler blowdown process, which includes a bottom blowdown and a surface blowdown. The bottom blowdown process involves getting rid of undissolved solids that have built up along the bottom of the boiler. In comparison, the surface blowdown process is meant to remove dissolved solids and high amounts of hardness that can be found in the boiler water. The suspended solids that can be removed during the bottom blowdown process include:

  • Iron
  • Silica
  • Phosphorous
  • Copper
  • Magnesium and calcium salts

On the other hand, skimming the surface of the water with the surface blowdown process will allow you to remove dissolved solids like:

  • Phosphate and silica
  • Potassium
  • Sodium
  • Magnesium
  • Soluble calcium
  • Chloride

It’s very important that you regularly perform surface blowdown to get rid of dissolved solids before they cause a system malfunction or other serious problems. Once enough dissolved solids build up on the surface of the water, it’s possible that the contaminated water would get into the boiler’s steam system, which would result in serious damage to some of the equipment that operates on steam. This equipment could extend to steam traps, steam turbines, and heat exchangers.

The frequency in which you perform the blowdown process depends on the quality of the feedwater that you use during this process. If the quality of your feed water is high, the bottom blowdown process may only need to be performed on a weekly basis. On the other hand, poor feed water could require you to perform this process daily to ensure that the dissolved solids in the boiler water don’t accumulate to dangerous levels. The steps involved with the bottom blowdown process include:

  • Start by opening the quick-opening valves, which are situated close to the boiler.
  • There should also be a slow-opening valve that must be open.
  • At this time, your water management consultant should help you determine what the blowdown process should look like. In most cases, it involves slowly opening and closing the single slow-opening valve until you have reached the desired results.
  • The slow-opening valve can now be closed.
  • The quick-opening valves can now be closed.
  • At this point, the slow-opening valve should be reopened to effectively drain the line that connects the slow-opening valve with the quick-opening valves.
  • Complete the process by closing the slow-opening valve.

As for the surface blowdown process, a pipe will be sent into the upper portion of the boiler at a position that’s six inches below the water surface. While the boiler is in operation, the pipe should always be kept below the water surface. A flow-throttling valve typically controls the rate of flow for the boiler water as it gets sent into the pipe. Consider using an automatic blowdown controller to keep the dissolved solids in the water at optimal levels.

Boiler Blowdown on Wastewater Treatment

boiler blowdown on wastewater treatmentWhen you want to treat the wastewater that occurs during the blowdown process, there are several things you should keep in mind. For one, the wastewater properties depend on how contaminated the water is and if any pre-treatment occurred before the full treatment process began. Before the water is sent to the sewers, there are numerous aspects of the water that must be adjusted, which include the pH levels, the amounts of dissolved solids in the water, and the water temperature. Blowdown wastewater can also be reused in certain situations.

Blowdown Management Treatments

In the event that you want to treat the wastewater that’s created during the blowdown process, there are several options you can use for blowdown management. These options include:

  • Discharge the water to a wastewater treatment facility – This would require you to perform pre-treatment on the water
  • Zero liquid discharge – This is a unique process that involves the comprehensive treatment of the wastewater so that it can be reused without needing to worry about liquid discharge
  • Treatment and reuse – The water reuse option that you use depends on water availability and water reuse laws in the surrounding area
  • Discharge to nearby surface waters – This option depends on the overall water quality

Before performing treatment on your boiler water, keep in mind that this stream is more difficult to treat than others. If you want to properly treat boiler blowdown, you will need to use several different technologies. Likely the best technology to use during this process involves a reverse osmosis system. With this system in place, dissolved solids can be separated from the water, which helps to create a premium permeate. Some of the pre-treatment solutions you may need to use include pH adjustment, ion exchange, softening, and filtration. The many benefits that come with treating the boiler blowdown include:

  • Less maintenance requirements
  • Consistent water quality
  • Less corrosion and fouling
  • Less chemicals

Why You Need to Blowdown Your Boiler

There are numerous reasons why you should blowdown your boiler on a regular basis, the primary of which is that it will allow you to keep your boiler at peak or near-peak efficiency. While it’s possible to prevent dissolved solids from getting into your boiler by treating the feed water and makeup water, there will invariably be some dissolved solids that get into the water no matter what preventive measures you take.

By routinely getting rid of water hardness and dissolved solids, the performance of your boiler will be maximized. You’ll also notice that repair and maintenance costs are relatively low as a result of performing boiler blowdown. As touched upon previously, the frequency at which boiler blowdown occurs depends on what the boiler is being used for and how much the water is treated. In general, you should expect to complete the boiler blowdown process anywhere from once a week to once every day.

If dissolved solids are left in your boiler, the solids will harden, which will result in the accumulation of sludge along the boiler surfaces. The heating surfaces will effectively become insulated when sludge and scale develops, which could result in the pressure vessel failing. The boiler water could also get into the steam, which may damage the piping and surrounding equipment. Because of the amount of damage that can occur if you don’t perform boiler blowdown on a regular basis, it’s highly recommended that you look into the blowdown guidelines that your boiler comes with.

Posted by Sensorex on May 3, 2021

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