What is silica in a boiler?

Silica is the only boiler water salt which vaporizes at pressures below 2400 psig. It can vaporize at pressures as low as 400 psig. The solubility of silica in steam increases with increased temperature: silica becomes more soluble as steam is superheated. Deposits are formed when steam is cooled by espansion.

Why do we test for silica in boiler water?

The silica monitoring in the boiler drum is one parameter which can be used to control blowdown. Silica monitoring provides a good indication of the overall steam purity level provided by the drum boiler, and subsequent action is required to avoid deposition of silica on the superheater and turbines.

How is silica removed from boiler water?

Lime softening is one of the most common methods for removing silica from water such as make up to cooling towers, make up to boilers or boiler blow down water. Lime softening utilizes the addition of lime (calcium hydroxide) to remove hardness (calcium carbonate and magnesium carbonate) ions by precipitation.

What is reactive silica and colloidal silica?

The key difference between colloidal silica and reactive silica is that colloidal silica is the polymeric form of silicon, whereas reactive silica is the non-polymeric form of silicon. This substance forms when silicon and oxygen react with each other and another metal or mineral.

What is the formula of silica?

SiO2
Silicon dioxide/Formula

What is silica water?

Silica is a hard, glassy-like mineral that is found dissolved in water as a result from the bedrock it passes through, like sandstone and granite. In well and surface water, it can range from 1-100 parts per million as dissolved (reactive) or undissolved (colloidal) silica.

What is total silica?

The “Total Silica” content of a water is composed of “Reactive Silica” and “Unreactive Silica”. Reactive silica (e.g. silicates SiO4 ) is dissolved silica that is slightly ionized and has not been polymerized into a long chain. Reactive silica is the form that RO and ion exchange chemists hope for.

Does RO remove silica?

Reverse osmosis (RO) is by far the most efficient way to remove colloidal and dissolved silica, which can be found in high concentrations in brackish water. The presence of silica and its ability to foul membranes limits the use of silica… plant.

How many types of silica are there?

There are two forms of silica – crystalline and noncrystalline. Crystalline silica is a bigger worry for the health of our lungs. The most common form of crystalline silica is quartz, which is found in sand, gravel, clay, granite, diatomaceous earth, and many other forms of rock.

What are the many different forms of silica?

The various forms of crystalline silica are: α-quartz, β-quartz, α-tridymite, β-tridymite, α-cristobalite, β-cristobalite, keatite, coesite, stishovite, and moganite (NIOSH, 2002).

How much silica is safe in water?

The maximum silica concentration in water is equivalent to 9.2 mg silica per 100 g (about 3.5 oz) of water, less than the amount found in dried fruits and breakfast cereals.

What is sand silica?

Silica sand is granular material that contains quartz and minute amounts of coal, clay and other minerals. It is also known as quartz sand and industrial sand, and is largely used in several construction applications. The presence of silica sand on metal materials can be a source of crevice corrosion on those metals.

What is the type of silica in boiler water?

There are two types of silica in boiler water; reactive silica and non-reactive silica or what is also called as the colloidal silica. The reactive silica can be removed by a process called ion exchange whereas non reactive silica is not removed by exchange.

What is the average silica content in water?

Silica, in amounts ranging from less than 1 to over 100 ppm, is found in all natural water supplies. In rain hail and snow, silica content range from 1 to 2.8 ppm. In the analyses of various surface and ground waters, silica content range from 1 to 107 ppm.

What are the three types of silica?

The three common kinds of silica are soluble, colloidal and particulate. The standard test for the analysis of silica in water is a rapid technique based upon the blue reduced silicomolybdate complex.

How does vapour silica carryover occur in boilers?

The conditions under which vapour silica carryover occurs have been investigated and documented. It has been demonstrated that for any given set of boiler conditions using demineralized or evaporated quality make up water, silica is distributed between the boiler water and the stream in a definite ratio.