CHEM NET EM
WHAT IS CHEM NET EM?
It has extensive application in on-line cleaning of fouled fireside heat transfer surfaces of boilers and furnaces. CHEM NET EM also helps in minimizing the problems of corrosion.
The key word in the description is “on line”. This means that the cleaning can be carried out without shutting down the boiler or furnace. For most users this is a critical benefit since organizations can ill afford an unscheduled shutdown of the equipment for cleaning.
FOULING AND ITS EFFECTS
Fouling refers to the formation of deposits on the heat transfer surfaces of boilers and furnaces. The deposits could be soot, sticky carbon and low melting point ash.
A certain level of fouling is inevitable in most boiler/furnace applications where coal or oil is used as the fuel.
Obviously the nature and the severity of the fouling depends on the characteristics of the fuel being used. For example if the fuel used is a coal with a low ash fusion temperature, fouling due to low melting point ash, particularly in the high temperature zones of the boiler, could pose a significant problem.
When oil is used as the fuel, carbon deposition, the consequence of incomplete combustion, could be the predominant cause of fouling. Most boiler installations follow a protocol of soot blowing to remove deposits on heat transfer surfaces. However soot blowing has limited effectiveness when the deposits formed are strongly adhesive.
1.Loss of fuel efficiency, manifested by elevated exit flue gas temperatures indicating high stack losses.
2.Fouling poses many problems to boiler/furnace operators. These include
3.Loss of capacity
4.Need for unscheduled shutdowns
5.Long cleaning cycles Imbalances in heat transfer leading to increase in the requirement of desuperheating sprays. For instance, if the firebox of a boiler gets fouled more heat will be needed to generate steam. The flue gas exiting the furnace will be at a temperature higher than the designed level. This, in turn, will result in excessive heat transfer in the super heaters. Higher than design level steam temperatures will result. This is not acceptable for turbine operation. Desuperheating sprays for the steam are therefore required.
All the foregoing has financial implications
SOOT BLOWING VERSUS CHEM NET EM TREATMENT
Soot blowing is the commonly accepted practice followed for removing deposits formed on heat transfer surfaces. However soot blowing is effective mainly for soft sooty deposits, which can be easily dislodged and blown away. Soot blowing is much less effective for sticky carbon deposits and those formed by the fusion of low melting point ash on the heat transfer surfaces.
CHEM NET EM treatment, on the other hand, is effective for removal of all types of deposits.CHEM NET EM is a type of chemical soot blowing. CHEM NET EM works through chemical reactions, which cause deposits to be effectively neutralized and blown away with the flue or dropped.
CHEM NET EM TREATMENT
CHEM NET EM, in the form of an aqueous solution, is injected into the flue path of the boiler/furnace. The injection is done at a point where the flue temperature is greater than 500°C. Injection is done by special lances and nozzles. The driving force for the injection is compressed air at a pressure of 5 to 6kg/cm2. If a compressed air facility is not readily available at the site a pump may be used as an alternative. However it must be assured that the injection pressure is 5 to 6 kg/cm2.
On injection into the hot zone, CHEM NET EM decomposes and vaporizes. The vapours travel to all parts of the boiler/furnace. It is these vapours of CHEM NET EM that, by chemical action, loosen and free adhering deposits.
CHEM NET EM, on decomposition, forms magnesium oxide (MgO), NO2, N2O and water vapour. The MgO neutralizes low melting point ash deposits by forming corresponding magnesium derivatives. The NO2 and N2O serve to oxidize carbon deposits forming carbon dioxide and elemental nitrogen.
The MgO also forms a grey protective layer on the heat transfer surfaces and this helps in preventing, to some extent, further deposits of unburnt carbon and low melting point ash.
If any sulphuric acid forms due to the sulphur in the fuel the MgO neutralizes this to form magnesium sulphate. Chem Net EM treatment, while ramping down for shutdown or ramping up after start up, will significantly reduce the probability of corrosion. It is during the shutdown and start up processes when there is maximum likelihood of flue temperatures falling below the dew point and, therefore, the greatest risk of corrosion.
If fuel contains vanadium the vanadium gets converted to vanadium pentoxide on combustion. Vanadium pentoxide acts as a catalyst for converting sulphur dioxide to sulphur trioxide. Sulphur trioxide reacts with water vapour to form sulphuric acid.
CHEM NET EM reacts with vanadium pentoxide to form magnesium vanadate. Chem Net Em therefore removes the catalysing agent that promotes sulphuric acid formation.
In some boilers there is the problem of hot spot corrosion. Hot spots are formed when low melting point ash forms a hard insulating layer on the tube surface. Hot spots can lead to tube puncture. CHEM NET EM treatment removes low melting point ash deposits thus minimizing the possibility of hot spot corrosion.
DOSAGE OF CHEM NET EM
Two levels of CHEM NET EM need to be considered:
1.For “clean up”
2.For “keep clean”
The “clean up” dosage is applicable for treatment of a dirty system.
The requirement of CHEM NET EM is computed as 0.3 litres of CHEM NET EM concentrate per tonne of fuel consumed over 10 days. Thus if clean up is required of a boiler system consuming 50 tonnes per hour of coal the quantity of CHEM NET EM is 50 X 24 X 10 X 0.3 = 3600 litres.
The computed quantity of CHEM NET EM is to be intermittently injected over a period of time – say 8 to 10 days.
If only a section of the boiler is known to be fouled the dosage of CHEM NET EM can be logically scaled down. For instance if it is known that only the fire box of a boiler is fouled and the heat transfer area in the fire box is 50% of the total heat transfer area of the boiler the dosage applied can be 50% of the prescribed dosage.
When a boiler/furnace is clean and the aim is to sustain cleanliness the “keep clean” dosage of CHEM NET EM is applicable.
The monthly requirement of CHEM NET EM for keep clean is calculated as 0.1 to 0.15 litres of CHEM NET EM per tonne of fuel consumed in a 7 day period. Thus if a boiler system consuming 50 tonnes per hour of coal is to be kept clean the quantity of CHEM NET EM required per month would be 50 X 24 X 7 X 0.1 = 840 litres to 50 X 24 X 7 X 0.15 = 1260 litres.
SUPPLEMENTING CHEM NET EM TREATMENT
On occasion, while CHEM NET EM treatment may loosen the deposits on heat transfer surfaces, the force of the flue gas may not be adequate to carry these away. In such instances injection of compressed air or high-pressure steam after each injection cycle would be of value.
ADVANTAGES OF CHEM NET EM
CHEM NET EM provides the boiler operator with a number of benefits. These include:
1.The cleaning of the boiler/furnace is carried out on line without an unscheduled shutdown.
2.Improved energy efficiency. Stack losses will be reduced by CHEM NET EM treatment.
3.Restoration of lost capacity, in cases where loss of capacity is due to fouled heat transfer surfaces.
5.Increased interval between shutdowns, therefore providing greater system availability.
6.Reduction, if not elimination, of soot blowing operations. CHEM NET EM treatment can be considered a type of chemical soot blowing.
7.Reduced cleaning time when shutdowns are taken.
8.Improved safety since the equipment’s operation is restored to prescribed design parameters.
9.Minimization of the requirement of desuperheating sprays.
10.Reduced power consumption of FD and ID fans, since fouling increases pressure drops and therefore fan power requirement.
11.Reduced air pollution since the CHEM NET EM treatment reduces acid formation and, therefore the possibility of “acid smutting”.
The payback period for CHEM NET EM treatment would generally be much less than one month.
REFERENCE CHEM NET EM USERS
There are a large number of CHEM NET EM. These include:
- TATA POWER, Mumbai – use on a 500 MW coal and oil fired boiler
- TATA Chemicals, Mithapur- use on coal fired boilers for power generation
- Various refineries of Indian Oil Corporation for use on process furnaces.
- Chennai Petroleum Corporation Ltd., Chennai
- Chandrapur Super Thermal Power Station – used on 500 MW coal fired boiler.
- OPG Power Generation Pvt. Ltd., Chennai – used on 80 MW coal fired boiler.
- MALCO – used on 4 * 35 MW coal fired boiler.
- BPCL KOCHI REFINERY
- BPCL MUMBAI REFINERY
- JSW SALEM
CHEM NET EM SUPPLY AND SERVICE
CHEM NET EM is a proprietary product of Neo Petcon India Pvt. Ltd.
Neo Petcon India Pvt Ltd. offers CHEM NET EM users in India a range of services. These include:
- CHEM NET EM application survey.
- Provision of lances and nozzles for the CHEM NET EM injection operation.
- User assistance in operations related to CHEM NET EM injection.
- User assistance in analysing system performance data.
- User assistance in developing protocols for CHEM NET EM application.
- Comprehensive user training in relevant CHEM NET EM technology and operations.
- Making available the services of experts where required.