create csv file from dataset in asp.net

anyone can help me to create the .CSV files from the dataset ds11, from the following code...
int _count = ListSeCh.Items.Count;
        if (_count != 0)
        {
            DataTable dtTemp = new DataTable();
            dtTemp.Columns.Add("Id", typeof(string));
            dtTemp.Columns.Add("Name", typeof(string));
            for (int j = 0; j <= _count - 1; j++)
            {
                DataRow dr;
                ...