time zone not getting saved in the database

Using rails 2.3.9 and ruby 1.8.7
I am trying add time zone in the site according to user’s time zone (selected by the user from the drop down of time zones)Code is done as follows, but time zone is not getting saved in the database.
IN Application Controller
before_filter :set_time_zone
def set_time_zone
Time.zone = current_user.time_zone if current_user

IN View form(haml)
f.time_zone_select :time_zone, ActiveSupport::TimeZone.all.sort

IN Environment.rb
config.time_zone = ‘UTC’

IN User table added time_zone as string column

To summarise, you have a time_zone string column in the database, but
you say that it is not getting saved to the database. First have a
look in the application log to see whether the zone is getting passed
when you click on the submit link for the form. If that looks ok then
use ruby-debug to break into the create or update method to see
whether params is setup ok and whether the User. See the Rails Guide
on debugging if you do not know how to do this.