out of memory - no sort

I am trying a simple
        access of a table and get an out of
          memory error.  How do I avoid this issue.  It seems I
        have some configuration set wrong.

        Our system has 24GB of memory and is dedicated to the postgres
        database.

        Back ground information

        aquarec=> explain analyze verbose select * from ens_memb;

                                                       
QUERY

PLAN                                                       


--------------------------------------------------------------------------------------------------------------------------
         Seq Scan on ens_memb  (cost=0.00..719893.12 rows=32216212
        width=62) (actual time=4.954..37513.377 rows=32216154 loops=1)
           Output: id, shefpc, bwmon, ewmon, pb, tb, cdate, vdate,
        source, tyr, val
         Total runtime: 39588.386 ms


#------------------------------------------------------------------------------
        # RESOURCE USAGE (except WAL)
#------------------------------------------------------------------------------

        # - Memory -

        shared_buffers =
6144MB                # min 128kB 

                                       
#(change requires 
        restart)
        #temp_buffers =
8MB                    
#min 800kB 
        max_prepared_transactions = 5           # zero disables the
        feature

                                       
#(change requires 
        restart)
        # Note:  Increasing max_prepared_transactions costs ~600 bytes
        of shared memory
        # per transaction slot, plus lock space (see
        max_locks_per_transaction).
        # It is not advisable to set max_prepared_transactions nonzero
        unless you
        # actively intend to use prepared transactions.
        work_mem =
48MB                        
#min 64kB 
        maintenance_work_mem = 256MB            # min 1MB
        #max_stack_depth =
2MB                 # min 100kB 

        # - Kernel Resource Usage -

        #max_files_per_process = 1000           # min 25

                                       
#(change requires 
        restart)
        #shared_preload_libraries = ''          # (change requires
        restart)

        # - Cost-Based Vacuum Delay -

        #vacuum_cost_delay =
0ms               # 0-100 milliseconds 
        #vacuum_cost_page_hit = 1               #
0-10000credits 
        #vacuum_cost_page_miss = 10             # 0-10000
credits
        #vacuum_cost_page_dirty = 20            # 0-10000
credits
        #vacuum_cost_limit =
200               # 1-10000 credits 

        # - Background Writer -

        #bgwriter_delay =
200ms                # 10-10000ms
between
        rounds
        #bgwriter_lru_maxpages = 100            # 0-1000 max
buffers
        written/round
        #bgwriter_lru_multiplier = 2.0          # 0-10.0 multipler on
        buffers scanned/round

        # - Asynchronous Behavior -

        #effective_io_concurrency = 1           # 1-1000. 0 disables
        prefetching


#------------------------------------------------------------------------------
        # WRITE AHEAD LOG
#------------------------------------------------------------------------------

        # - Settings -

        #fsync =
on                            
#turns forced 
        synchronization on or off
        #synchronous_commit =
on               # immediate fsync at 
        commit
        #wal_sync_method =
fsync               # the default is the 
        first option

                                       
#supported by the 
        operating system:

                                       
#  open_datasync 

                                       
#  fdatasync 

                                       
#  fsync 

                                       
#  fsync_writethrough 

                                       
#  open_sync 
        #full_page_writes =
on                 # recover from
partial
        page writes
        wal_buffers =
8MB                      
#min 32kB 

                                       
#(change requires 
        restart)
        #wal_writer_delay = 200ms               #
1-10000milliseconds 

        #commit_delay =
0                      
#range 0-100000, in 
        microseconds
        #commit_siblings =
5                   #
range1-1000 

        # - Checkpoints -

        checkpoint_segments =
32               # in logfile segments, 
        min 1, 16MB each
        #checkpoint_timeout = 5min              #
range30s-1h 
        #checkpoint_completion_target = 0.5     # checkpoint target
        duration, 0.0 - 1.0
        #checkpoint_warning = 30s               #
0disables 

        # - Archiving -

        #archive_mode = off             # allows archiving
tobe done 

                               
#(change requires restart) 
        #archive_command = ''           # command to use to archive a
        logfile segment
        #archive_timeout = 0            # force a logfile
segmentswitch 
        after this

                               
#number of seconds; 0 disables 

#------------------------------------------------------------------------------
        # QUERY TUNING
#------------------------------------------------------------------------------

        # - Planner Method Configuration -

        #enable_bitmapscan = on
        #enable_hashagg = on
        #enable_hashjoin = on
        #enable_indexscan = on
        #enable_mergejoin = on
        #enable_nestloop = on
        #enable_seqscan = on
        #enable_sort = on
        #enable_tidscan = on

        # - Planner Cost Constants -

        #seq_page_cost =
1.0                   #
measuredon an 
        arbitrary scale
        random_page_cost =
3.0                 # same scale
asabove 
        #cpu_tuple_cost =
0.01                 # same scale
asabove 
        #cpu_index_tuple_cost = 0.005           # same scale as above
        #cpu_operator_cost = 0.0025             # same
scaleas above 
        effective_cache_size = 12288MB

        # - Genetic Query Optimizer -

        #geqo = on
        #geqo_threshold = 12
        #geqo_effort =
5                       
#range 1-10 
        #geqo_pool_size =
0                    
#selects default based 
        on effort
        #geqo_generations =
0                  # selects
defaultbased 
        on effort
        #geqo_selection_bias = 2.0              #
range1.5-2.0 

        # - Other Planner Options -

        default_statistics_target = 100         # range 1-10000
        #constraint_exclusion = partition       # on, off, or partition
        #cursor_tuple_fraction = 0.1            # range 0.0-1.0
        #from_collapse_limit = 8
        #join_collapse_limit =
8               # 1 disables collapsing 
        of explicit

                                       
#JOIN clauses