Shares of Tennant Co. rose almost 12 percent and hit a 12-month high after the company posted better-than-expected second-quarter sales and earnings, fueled mostly by continuing robust demand for its eco-friendly cleaning machines.

The stock closed at $44.25 a share on unusually heavy volume of about 134,000 shares.

The Golden Valley-based manufacturer of floor-scrubbing machines posted a 21 percent increase in sales to $201.3 million for the period ended June 30. Excluding special charges of 26 cents a share, adjusted earnings increased 75 percent to $10.9 million, or 56 cents a share.

Analysts had estimated sales of $190.1 million and adjusted earnings per share of 47 cents.

Sales of scrubbers that use the company's proprietary chemical-free ec-H2O technology rose 85 percent in the quarter. In the first six months of 2011, sales of scrubbers equipped with the technology totaled $67 million, and Tennant expects them to be in the range of $130 million to $140 million for the year. The technology converts water to a cleaning solution.

"Our ec-H2O technology has firmly established Tennant as an innovator in sustainable, water-based cleaning," said CEO Chris Killingstad.

Tennant also raised its sales and earnings forecast for the year. Excluding special charges, the company now expects adjusted earnings per share in the range of $1.95 to $2.05 on sales of $750 million to $765 million. Previously, the company anticipated adjusted earnings per share of $1.75 to $1.95 on sales of $710 million to $730 million. That compares with last year's adjusted earnings of $1.31 per share on sales of $667.7 million.

Susan Feyder • 612-673-1723