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Introduction
Some deposit formation on the fire-side heat transfer surfaces is inevitable in fuel-fired heating equipment like refinery furnaces or boilers in the process industry or power stations.
The deposits, depending upon the nature of the fuel and the combustion systems, form in the furnace section or on the extended heat transfer surfaces like the studded tubes in the convection banks in the refinery furnaces or the economizer superheater section of power station boilers or in the air preheaters. The deposit formation gradually reduces the heat transfer efficiency, leading to higher fuel consumption and a reduction in the boiler or power plant capacity or in the refinery furnaces. A shutdown for cleaning is a very high cost to the industry because it implies vast production loss. Therefore, a need has been felt for cleaning the deposits online or without a shutdown.
CHEM NET EM is our propriety formulated product developed with improvements of earlier products used for effectively addressing the range of deposits, especially low melting point ash and residues of unburnt carbon. It is available to the export market.
Why CHEM NET EM?
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CHEM NET EM is an aqueous solution of chemicals that are injected into the flue gas at a point where the temperature is above 450°C. CHEM NET EM dissociates into its components, which perform the following cleaning functions: Convert the low melting point ash, which is sticky, into dry high melting point magnesium derivatives which either fly away with the flue gas or drop down to the bottom of the furnace. One dissociated component is a potent oxidising agent that cleans the carbon deposits by gradual, slow oxidation..
Method of Injection
CHEM NET EM has to be injected as a fine spray for rapid evaporation and dissociation into the components that address the deposits. CHEM NET EM has to be injected through openings around the periphery of the boiler to ensure that it reaches different parts of the fouled sections along with the flue gas. CHEM NET EM is injected through high-temperature resistant lances and nozzles to achieve a fine spray, typically with a pressure of 7 kg per cm2.
Some of the main benefits provided by CHEM NET EM
Chemical Soot Blowing
CHEM NET EM is a kind of chemical soot-blowing. Mechanical or steam soot blowing can often not remove very sticky deposits, especially of low melting point ash and unburnt carbon, inflow areas of severe constrictions. CHEM NET EM will drastically loosen the adhered deposit and clean up the surfaces if the flow velocities are high enough or complemented with mechanical steam soot blowing but with as reduced frequency as usual.
Protection against acid corrosion
CHEM NET EM provides a magnesium oxide coating on the tube's external surface. Therefore, CHEM NET EM can be used before a scheduled shutdown to prevent corrosion due to the flue gas and the high sulphur oxides present cooling below the dew point and causing acid corrosion.
Protection against Abrasive wear
CHEM NET EM can be a very effective method with the coating of magnesium oxide to reduce the abrasive wear of the tubes with the high velocity of abrasive ash present in the flue gas or unavoidable clinker in the streams in the waste heat recovery boilers, as an example in cement plants.
Range of Applications of CHEM NET EM
Deposit formation is inevitable in almost all fired heaters. The extent of deposit formation may vary with the nature of the fuel. For example, oil, coal, and biomass firing lead to more deposits than gas. Biomass-fired boilers rapidly have excessive deposit formation, leading to frequent shutdowns for cleaning as the desired steam generation capacity is not achieved. CHEM NET EM drastically reduces the deposit formation and deposit adherence to the heat transfer surfaces, thus substantially extending the run periods between shutdowns.
Requirement of Openings
CHEM NET EM can prevent deposit adherence and clean up already formed deposits, but it has to reach the surfaces that are to be cleaned and kept clean. It is injected into the flue gas path. Enough openings around the periphery of the furnace, if possible, at multiple levels are required for the chemical to reach the dirty surfaces and ensure effective cleaning. In applications such as biomass-fired boilers where the deposit accumulation is very rapid, typically in a few hours, continuous injection of CHEM NET EM is considered desirable and suitable systems can easily be provided for continuous injection.
Dosage
The Dosage of CHEM NET EM is determined based on the surface area required to be cleaned and the quantum of deposit already present and is likely to form. The surface area directly correlates with the furnace's heat duty and quantity of fuel fired. The dosage of CHEM NET EM and the total amount to be injected for a short duration for clean-up operation and the lower dosage for continuous keep clean operation is determined based on the fuel firing rate and the proportion of the surface area of the heater, which has excessive fouling.
The requirement of CHEM NET EM is computed based on the surface area of the heater required to be cleaned, the amount of deposit, the fuel used, and the period for which the injection is to be done, typically 7 to 10 days, depending upon the openings available to have good access to the dirty surfaces. A high dosage is required if very sticky or clinker deposits are already formed. The dosage, the period of injection and the frequency have to be customised based on the application and the operating practices.
Cost Effectiveness
CHEM NET EM is typically so cost-effective that the benefit of energy saving and high capacity allows the payback of less than a few months.
