Mechwell Industried Ltd. MWI

FAQ for CAVT Test

What is CAVT ?

Ans:- It is cold air velocity test

Where it is done ?

Ans:- IT is done in second pass of the boiler in cold condition / boiler shut down.

What are the benefits of this activity ?

Ans:-

Better gas flow distribution
Better heat transfer
Eco out let temperature is reduced
Boiler tube erosion will be reduced / prolonged
Attemperation may be reduced due to heat transfer.
Boiler tube leakage reduced.

What are the conditions to carry out CAVT ?

Ans :--

Boiler to be shut down condition
Atmosphere temperature inside the boiler.
Boiler is in boxed condition.

What are the requirement from client for CAVT ?

Ans :--

Air flow should be 80% of the MCR
I D & F D fans are in running condition
Boiler to be boxed up condition
Minimum draft to be maintained inside the boiler i.e. 5 to 8 mm of W.C..
Scaffolding at screen tube location is required.
Scaffolding at any other location where distance between two banks are more than two meters.
Boiler parameters are to be maintained constant during testing

What is the procedure for CAVT ?

Ans :-- Procedure is attached herewith

Can output be guaranteed of CAVT ?

Ans :-- Yes, Benefits are there , subject to carrying out activity in every shut down.

What is justification of the budget of CAVT ?

Ans.:-- Reduction in boiler tube leakage and loss of generation due to tube leakage . cost will justify budget.

Can it be done in any Boiler ?

Ans :-- Yes , but on considerable size of boiler.

What do the tables in report indicates?

Ans :- There are three tables in the repot for each location

It is actual readings taken in the boiler in meters per seconds.
It is normalized velocity calculated on the basis of table A
It is the predicted velocity at MCR parameters of the boiler

What is MCR velocity ?

Ans :- This is the maximum continues rating of the boiler

What is normalized velocity ?

Ans :- It is a direct deviation with reference to average velocity.

What is the type of instruments used ?

Ans :-- Instrument used for this testing is "HOT WIRE ANAMOMETER "

How much time is required for this test ?

Ans :-- Four to five hours depending upon size of boiler.

How much time is required for implementations of recommendations ( EMS Screens erection)?

Ans :-- Five to six days after shifting the material at site , also it depends on size of boiler.

How many persons are required for the test ?

Ans :--Two to three teams , one team consist of two persons.

What are the appliances used during testing ?

Ans :-- Mask , plane goggle, head lamp , hand gloves , writing pads, required formats like CAVT location drawing, reading formats , control room data formats , pen ETC

How does tube erosion occur in running boiler ?

Ans :- Tube erosion will be due to fly ash abrasive nature and velocity at that location

Where tube leakage are expected more?

Ans :-- It is in second pass of the boiler due to boiler tube resistance , and the temperature, abrasive nature is more effective at lower temperature.

How MCR is calculated?

Ans :- It is a numerical calculation , gas flow generated by quality & quantity of coal burns passing through opening area in second pass ( area without tube minus area with tube) - This gas velocity multiply by local normalized velocity , gives the MCR velocity of that location.

What should be the frequency of this test ?

Ans :-- It should be carried out in every overhaul of the unit to know changes in flow and effect of any maintenance during the span of one year.