Mayor Rahm Emanuel on Thursday hired a private consulting firm to consolidate and overhaul city contracts and wring at least $25 million in savings out of $500 million in purchases.

The savings generated by Accenture are expected to come from renegotiating some contracts, rebidding others and combining purchases by individual city departments to get a cheaper bulk price.

The contract calls for the company to review $500 million in contracts and get 10 percent of the first $70 million in savings, with a smaller percentage after that. But Accenture will not get paid at all until Chicago taxpayers get their check.

“Some of it will be better coordination. Some of it will be in better negotiations with who we’re buying from. Some will be in bulk purchasing that we’re seeing already between the city and county. They buy salt. We buy salt. They buy natural gas. We buy natural gas. If you’re buying in bigger quantities, you can find savings,” Emanuel said.

“So, it’s not gonna be in one way. It’s gonna be in multiple ways, but by being very aggressive in the contracting. . . . They don’t just identify [savings]. They’ve got to make sure we get it. That’s what’s important — that we get that $25 million in savings, not just identify $25 million in savings.”

City Hall purchases nearly $2 billion in goods and services each year. Accenture has estimated that it can easily save $25 million on $500 million of those contracts — and Emanuel said he’s convinced of it, based on the company’s track record.

According to Emanuel, Accenture’s technology and procurement expertise saved $140 million for the state of Pennsylvania, $30 million for the state of Ohio and $86 million for New York City’s Department of Education.

Some of the savings in Pennsylvania came after the company found that a hospital in Allentown was paying $23.20 for a case of ketchup, while a prison in another part of the state was paying just $12.66. They were able to get the lower price for the entire state by centralizing the contract, officials said.

“It was high time that Chicago used a Chicago-based company to find those savings for its taxpayers,” the mayor said during a news conference at the Chicago Department of Transportation bridge shop at 3124 S. Sacramento.

Former Mayor Richard M. Daley twice asked city contractors to voluntarily reduce their prices, but all but a handful of companies refused.

Chief Procurement Officer Jamie Rhee said the Accenture contract is a whole new wrinkle — and one that’s far more likely to succeed because the company does its homework.

“It was a voluntary renegotiation [under Daley]. This is going to come with some market data that says, ‘Listen. We believe we can get this cheaper and, if you’re not willing, then we will “terminate for convenience,” ’ which is in all of our contracts, and go back out to bid . . . or tap into another agency’s contract that has a better price,” Rhee said.

“They also look around and see, ‘Did we bid this contract out when the market was high and now the index is low?’ Folks are very hungry out there right now. It’s a tough market. Maybe a contract is a year-and-a-half old, the index [then] was really high and it’s fallen now, so it’s a good time to go back out and bid or re-negotiate with the vendor to say, ‘You give us this or we’re gonna have to go back out to the market.’ ”

The Accenture contract is the latest in a series of steps Emanuel has taken to overhaul city contracting.

He is also using reverse auctions to get a better price while reining in no-bid contracts and posting all of them on the Internet. And the mayor has asked former Chicago Park District Board President John Rogers to recommend ways to boost the paltry percentage of city contracts that go to African Americans.