What is the difference between normal NAND gate and Schmitt trigger NAND ?
Does it is interchangeable in an application ?

 

Yes. Visualize a convention NAND gate with a simple non inverting Schmitt trigger in front of each input.

 

Well, you can use a Schmitt-trigger NAND to replace a regular NAND in most cases; if the inputs have fast rise/fall times.

However, trying to use a regular NAND for a Schmitt-trigger NAND may cause problems, particularly if the input(s) to the gate have slow rise or fall times.