can we run linux kernel separately 2097

Sure you can.

But a kernel alone won't do much. It will just "spin its wheels" waiting for some process to start. Of course, even this is useful at times. The "stateful firewall" part of the kernel runs, even when there are no user processes running. It is conceivable that youcouldpreseed the kernelspace with a set of firewall rules (thus bypbutting the need for a userspace app to do so), and just run the kernel standalone to get a very secure (can't be altered or stopped) firewall.

FWIW, I've heard (legend? rumour? myth?) that even a stopped kernel (kernel panic which caused most task switching to fail) still ran as a pbuttable firewall. The rules had been loaded before the panic, and the network ISR still triggered them whenever a packet was received.

OTOH. if you are more concerned with custom building a linux system, and want to "start from scratch" without basing your system on one specific distribution, you can always look into the "Linux from Scratch" meta-distribution (you compile everything from source, they just give you the guidance) or the GenToo distribution (similar to LfS, but they also give you the starter tools and a framework to build your system in).

HTH -- Lew Pitcher