July 28 (Reuters) - Solvay SA on Thursday raised its full-year guidance after the Belgian chemicals group beat second-quarter earnings expectations, boosted by strong demand across its key markets and price increases which helped compensate the rising cost of raw materials, logistics and energy.

The group, whose products range from base chemicals such as soda ash to speciality polymers, now expects its full-year underlying earnings before interest, tax, depreciation and amortisation (EBITDA) to grow organically at between 14% and 18%, while it had previously estimated a percentage increase in the mid- to high single digits.

It also projected its free cash flow at 750 million euros ($765 million), against an earlier forecast of more than 650 million euros.

Solvay had flagged a possible guidance hike last week, saying preliminary figures indicated its quarterly figures would come in "well ahead of expectations."

"The estimates reflect modest declines in demand consistent with the generally negative economic outlook and do not assume significant discontinuities related to the supply of natural gas particularly in Europe," the group said in a statement.

Like many European companies which now face uncertainty about new rounds of cuts in Russian gas supplies, Solvay has also put in place contingency plans for alternative sources of energy to protect production.

The group's "Plan B", Solvay Chief Executive Ilham Kadri said in an interview, includes adapting burners to use alternative fuels and rental of mobile backup boilers which run on liquefied natural gas(LNG), diesel, and coal.

Solvay's EBITDA rose 35% organically in the second quarter to 864 million euros, at the upper end of its own guidance range of 855-865 million euros.

Total sales, which increased 32.6% to 3.48 billion euros, were boosted by price hikes and higher volumes, which rose 26% and 6% respectively, the group said.

Analysts in consensus estimates provided by the company expected on average quarterly net sales of 3.10 billion euros and EBITDA of 683 million euros.

"We delivered in the last 12 months 1.6 billion euros in pricing, so we more than overcome the variable cost increases," Kadri said.

"We will continue to maintain the pricing we have, we will look at mechanisms to continue doing what it takes to defend our margin," she added. ($1 = 0.9806 euro) (Reporting by Dagmarah Mackos; editing by Jonathan Oatis)