It can since blockchain is just a way how to store data after all, though the banks must invent a way to get a system going to produce blocks of data and have them chained together. Some banks are already trying to integrate blockchain into their systems, and it's just a matter of time before a bank gets a fully-working system that uses blockchains for its own financial services. It's not really impossible, we just haven't seen a working one as of late.

thank for answering but what i am trying to ask is that , can bank sector do transactions on blockchain with creating the own crypto Currency  ?

Well said. Yes banks can run financial activities on blockchain without having their own crypto currency because blockchain can used to stored data, it can be used for security some classified information, can you used to distribute some information to the right people. The banks only have to understand and choose the size they want to use it for.

yes, it is possible the reason why many blockchain introduce a token (that you call cryptocurrencies) is to provide a means through which users of such platform pay for using the services (transaction charges, mining etc). for a private financial institution that wants to improve on managing and store a large amount of data. they may not need to create crypto but in case they need some external agent (such as miner) to keep the platform running then they will need to provide a way of incentivizing them and such is what happened in cases of some coin that are created by blockchain that is used for financial activities

It is easily possible. They can create their new network easily and progress with it. I think central banks can create and open for use all their national banks. So all banks use same network and make their transactions quickly.

If they think it globally, then they can use Bitcoin

Absolutely no, this is not possible, the blockchain technology must be backed by crypto currency, for any transactions to run on the system, it must have it's own coin. The whole idea behind crypto currency is to tokenize the transaction system, this could only be achieved when all transactions running on the blockchain has a token.

the answer is no.
others (except one) are misunderstanding the question since it is a bit strange. of course as others mentioned the technology is a different thing and they can adopt it without using the bitcoin or altcoins. but that is not what you are asking here?

first you need to know that there is nothing called "coin" in this technology. we only have a ledger that we store "transactions" in it. and then we call those transaction outputs as "coins". when you want to use this technology you have to do the same, meaning create transactions and store them in that ledger (like a database) so you are creating your own blockchain, your own transactions or your own "cryptocurrency"

So far, I know that banks have not used blockchain transactions and they do not think they will create a crypto coin in it because this is against the bank that has hated the existence of crypto, if it is true that banks will use the blockchain system without crypto currency

Definitely. Bitcoin and Blockchain are separate entity. What powers bitcoin though is blockchain technology. Just what others have pointed out, blockchain is sort of a ledger or database that can be used not just by the banking industry but other sectors that involves high volume of data to be stored like supply chain management or logistical system.