protected function _prepareCollection()
    {
        $collection = Mage::getResourceModel('sales/order_grid_collection');
        $this->setCollection($collection);
        $sales_flat_order_table = Mage::getSingleton('core/resource')->getTableName('sales_flat_order');
        $collection->getSelect()->join($sales_flat_order_table , 'main_table.increment_id = '.$sales_flat_order_table.'.increment_id', 'web4pro_abandonedcart_flag');
        $collection->addFieldToFilter($sales_flat_order_table.'.web4pro_abandonedcart_flag',array('eq' => 1));
        return parent::_prepareCollection();
    }