The two sentences given have almost the same meaning, but I think the second one could be rendered in English as "A refrigerator is located in the kitchen," stressing the location rather than the mere existence of the refrigerator. In general, the impersonal verb es geben means "there is" or "there exists", would almost always have an indefinite article when used with a singular, countable noun, and would not require a location. On the other hand, the reflexive verb sich befinden means "is located", can be used with a definite article or a proper noun, and would always include a location. In other words, if you're giving the location of a specific thing or person, then you could only use sich befinden.