'Net-zero' oven to revolutionise commercial baking

The UK has committed to achieving net zero greenhouse gas emissions by 2050. As part of this programme, funding has been made available to various industries to drive innovations that can help to push up efficiency and cut carbon footprints. At the moment, the baking industry relies almost exclusively on natural gas to fuel the ovens that turn out the consumer products we all enjoy, including things like cakes and biscuits. And therein lies an opportunity. Mark Williamson, an engineer, oven extraordinaire, and fellow of Queens’ College in Cambridge, has teamed up with the Ferrero Group - the company behind some of the biggest high street food brands - to break the mould and cook up a revolution in industrial baking. The new oven technology they’ve developed is electrically powered and over 80% efficient - at least twice as good as the traditional gas equivalent. It recovers back into the oven much of the energy that present processes throw away, and uses clever tricks of physics to push far more heat into the food than traditional techniques can. Mark invited me to an industrial estate on the outskirts of Cambridge to see the prototype in action…

Mark - It's all about net zero and saving energy in industrial baking, that's why you're here.

Chris - What is in front of me? We're in a big unit on this industrial estate and there is a machine—it looks the size of an underground train or a bus—in front of me. What is this?

Mark - Right, so this is an industrial baking oven, a continuous baking oven, about 30 metres long, and it's actually a baby. The industry has a lot of ovens that are 100 metres long, so although it looks big to you, this is a small one.

Chris - And what's novel here? What are you trying to do that breaks the model?

Mark - As everybody knows, there's a big drive to get away from fossil fuels, and what we've done here is build an oven that uses renewable electricity to bake food rather than natural gas.

In this oven, the first thing that we do is try to conserve the heat that goes into the continuous conveyor. This oven has a metal belt that runs through it. It's just over a metre wide and, in this case, about 25 metres long. Once it gets to the end, it comes all the way back again, so it's an endless loop, if you like, of metal.

Chris - Effectively a conveyor belt, because I can see it here going round very slowly, end to end. What's it made of?

Mark - Okay, so the belt is made of mild steel, which ends up being the right thing for producing this particular type of food, which in this case is biscuits.

Chris - Does it make a difference though, the fact that it's steel? You can embody a lot of heat energy in steel, so are you able to bring—effectively, because it's in a continuous loop—energy from the end of the oven that you'd throw away, can you get that back to the beginning in some respects and reuse it?

Mark - Absolutely, yes you can. To quote some numbers, just by saving heat in the oven conveyor, we've saved about 30 kilowatts.

Chris - Straight away, 30 kilowatts out of what? What would be the normal running consumption of an oven like this?

Mark - This oven, when it runs, is drawing about 110 kilowatts, so it's about 25% of it.

Chris - Is that why there's a generator throbbing out here? All these cables, are these yours?

Mark - Yes, they are, yes. We've got a very net-zero-unfriendly generator outside, giving us 120 kilowatts, because a typical factory unit like this has a supply of only about 35 kilowatts.

Chris - Good grief. So the biscuits—we can see they come off of the thing that basically presses out rows and rows of biscuits—they end up on the conveyor, there's the steel belt. Talk us through what happens next then, how do you actually cook them?

Mark - Okay, so once the biscuits—the dough—is on the steel belt, it goes into a tunnel, which is the oven basically, and inside the tunnel there are heating elements underneath the metal belt and heating elements on top.

Chris - Now when we've spoken about ovens in the past, you've made a lot of the fact that you can use different colours of light—effectively different wavelengths, different energies—to achieve different cooking intensities or effects. So is that happening here?

Mark - Absolutely, yes. Heating elements come in all sorts of different shapes and sizes. The cheapest ones—if you look inside your domestic oven and you see the grill—when it's on it might glow slightly red. That's about five or six hundred degrees centigrade, and it works in a domestic oven, but it's very limited in terms of what it can do, and specifically the radiated energy—the colour of the light as you explained it—it actually bounces off food that contains a lot of water. If we get those heating elements much hotter, and by that I mean 1,500 degrees centigrade instead of 500, a lot of the energy magically goes into the food instead of bouncing off.

Chris - And is that what you're doing here then? You're paradoxically making the elements hotter, but you actually save energy because more is absorbed by the food, so you use less
overall.

Mark - Exactly right, yeah.

Chris - How do you know though what's actually going on in there? Because you're at the stage where you're testing all this out, you've got a proof of concept, and this is government money, isn't it, that's paying to try and cut costs of manufacturing. How do you know, though, when you're doing tests like this, that it's doing what you think it is? What's your readout, apart from the biscuits that emerge at the other end either cooked to perfection or overdone?

Mark - We've got nearly 150 measurement points of temperatures, pressures, flows—all over the oven—and we have something special that's new. We actually have cameras looking inside the oven all the way down it at intervals, and the cameras in real time actually measure the colour of the top of the food and the dimension of the food itself. If you put dough into an oven, a biscuit will rise very quickly and get to almost twice its height, and then as it's nearly ready it starts to collapse again. That change in height profile is very useful if you're controlling a process. We don't think anybody else in the world has done this yet.

Chris - How else can you save energy though? Because presumably, if you've got an open end to an oven and stuff is going in at a cold end and there's a hot end, there's going to be a pressure difference and air is going to blow through. So how do you not lose all your heat from inside your oven—or do you? Do you just have to live with that?

Mark - One of the things you have to do in one of these ovens is make sure all the fumes from the baking don't come out into the workspace that's around the oven. So on the roof of the oven there's a series of chimneys, exhaust stacks, and what we do is bring those all together and we put them through what's called a heat recovery vessel. We spray cold water into the very hot flue gases that might be at 250 degrees centigrade, and what comes out the bottom is hot water that can be used in the bakery for things like washing or keeping chocolate tanks warm with a jacket. Those heat requirements would otherwise require a steam boiler.

Chris - If this performs the way that you are hoping, and you get the kinds of savings and heat recoveries that you think you can with this—if it all works—what kind of a difference do you think you could make to the energy bottom line of a big commercial baker?

Mark - We were required to do a quite substantial survey of our industry by the government to establish, if you like, the baseline—the benchmark—for how the industry performs energy-wise for these big ovens, and the number for that is somewhere around 38 to 40 percent thermal efficiency, compared with this oven, which we are currently measuring at about 82 percent. We've got enough data from this test unit that’s proved we've done it—we can do it.

Chris - And if one looks at the size of the industry, what sort of carbon saving might that translate into—back of the envelope?

Mark - This oven here uses about 110 kilowatts and the equivalent amount of natural gas would create about 20 tonnes a day of carbon dioxide^*.

Chris - But the proof is in the eating—and that's not a bad joke. The point is this is all about food, it's all about flavour, and people are not going to buy something that doesn't taste the way they've got used to it tasting. I hate when manufacturers change the recipe of biscuits that I've learned to love. So does it churn out food that I would not be able to distinguish from a gas-cooked biscuit?

Mark - Well, that's a very good question because food producers are very sensitive to that particular question.

Chris - As are the customers.

Mark - Yes, and they do not want to lose market share. So we've done a lot of work in the lab simulating the heating systems in this oven on a small, pilot plant scale, and food tasting panel tests to make sure that we've got a strong belief that we can dial this thing in, basically, to give us food that people cannot tell the difference.

Chris - And do you just stop at biscuits? Could you do anything with this or does it have its limitations?

Mark - I mean, if you like the physics of this, Chris, the way we're doing it—it has applications right across food, also ceramics, glass manufacture, paper manufacture. All those industries can do exactly what we've done and dial it in, if you like, to their particular product requirements.

* Note added in proof: An inaccuracy was picked up in the emissions calculations and it should be noted that: Natural gas produces CO2 at a rate of about 0.19 kg/kWhr. The oven documented in this report will use about 110kW, which is about 500 kg CO2 / 24 hour production day.  A much less efficient conventional gas fired oven would use about twice this. So the emissions reduction being achieved is 15-20 tonnes of CO2 per month, not per day as originally stated in the podcast.