Running a factory without gas: which heat loads move first, and in what order

Taking a factory off gas is a sequence, not a purchase. Sort the heat loads by output temperature, meter what each one consumes, move the block below 100°C onto a heat pump, and keep the fired plant for the duties that genuinely need it. Industrial piped natural gas in Gujarat cost ₹68 per SCM in June 2026, against ₹44.68 per SCM in Morbi two years earlier, so the price floor moved and stayed moved, and the loads that can leave gas are usually a larger share of the bill than the plant expects. Tetra Heat Pump, a product of Promethean Energy Private Limited, builds air source, water source and cascade machines delivering continuous output up to 120°C, with single units to 1,450 kW and multi-unit projects to 5 MW, which is the range that decides how much of that block can move in one step.

What do I do first when gas stops working?

Not a quotation. The first piece of useful work is a list of every heat load in the plant, with its output temperature and its measured consumption beside it. That list decides everything downstream: what can move, what cannot, how large the machine is, and what the electrical connection has to carry.

Most plants do not have it. What they have is one gas meter at the boundary and a boiler feeding a header, so the fuel bill arrives as a single number with no breakdown by duty. Until that number is split, every conversation about switching is a conversation about the boiler nameplate, not about the load, and a machine sized from a boiler nameplate is oversized, runs badly at part load and takes longer to pay back than it should.

If your boiler is rated in tonnes per hour, one TPH of saturated steam is roughly 583 kW of thermal duty. That is our own arithmetic and it is useful for a first pass, not a substitute for metering the individual loads.

The formal version of this exercise is an investment-grade energy audit. For an MSME with a Udyam ID in a notified cluster, ADEETIE runs from FY2025-26 to FY2027-28 and funds both the audit and the detailed project report, alongside interest subvention of 5% for micro and small units and 3% for medium ones, across 60 clusters and 14 sectors, with a condition to demonstrate 10% energy saving from the technology installed. Confirm on the scheme portal whether industrial heat pumps sit on its approved technology list before you put the subvention into a business case.

Which of my heat loads can actually come off gas?

The split is decided by output temperature and not by the industry you happen to be in. A pharmaceutical plant and a galvanising line have almost nothing in common commercially, and yet they arrive at very similar answers here.

Load	Output temperature	Where it goes
Alkaline degrease and component washing	55 to 80°C	Heat pump
Zinc phosphating	50 to 60°C	Heat pump
Clean-in-place and caustic wash circuits	70 to 85°C	Heat pump
Aqueous jacketed reactors	Up to 88°C	Heat pump
Galvanising degrease and flux tank	60 to 80°C	Heat pump
Air handling reheat after dehumidification	Below 100°C	Heat pump
Retort sterilisation	121°C saturated steam	Stays fired
Bake, cure and electrodeposition ovens	140 to 204°C	Stays fired
Spray dryer inlet	180 to 200°C	Stays fired
Alkyd resin polycondensation	150 to 280°C	Stays fired
Tempering and annealing	150 to 700°C, and 650 to 850°C	Stays fired

In a plant raising steam at pressure to serve a mixed header, the duties below 100°C are usually a larger share of the fuel bill than the plant expects, because steam raised at high temperature to feed an 80°C bath throws away most of the temperature it cost fuel to produce. That is the block to attack first, and a heat pump can take it without going anywhere near the ovens.

Sector by sector, the in-range and out-of-range loads are set out on the automotive, pharmaceutical and food and beverage pages.

What order does the work happen in?

There are eight steps, and the sequence in which you take them matters a good deal more than the speed at which you move. Skipping any one of the first four is what turns a retrofit into a rework.

Step	What it produces	What goes wrong if you skip it
1. Meter the loads	Consumption and output temperature per duty	The machine gets sized from the boiler nameplate
2. Draw the temperature line at 100°C	The block that can move, and the block that cannot	The scope creeps into oven duties the machine cannot serve
3. Find the heat source	A measured source stream, its temperature and its availability	The design falls back on ambient air when a warmer source was sitting in the yard
4. Check the electrical headroom	Spare sanctioned load, or the size of the enhancement needed	Commissioning stalls behind a connection application
5. Separate the low-temperature block hydraulically	A hot water circuit the heat pump can own	The heat pump ends up feeding a steam header and never sees its design conditions
6. Settle the capital and tax position	Depreciation and any scheme treatment agreed before the order	The tax position is discovered after the invoice, when it can no longer be structured
7. Install in parallel and tie in during a planned stoppage	A working loop with the boiler still live behind it	Production is exposed to a system nobody has run yet
8. Commission against the metered baseline	Measured performance at your conditions	Nobody can prove what changed, and the next project has no case

Step 6 has a specific Indian answer worth knowing early. Accelerated depreciation on this equipment is 40%, and heat pumps are named explicitly in Appendix I, item 8(ix) of the Income Tax rules, so the treatment is not something your auditor has to argue by analogy.

Step 6 is also where a project with a sound business case and no capital budget stalls, which is a different problem from a weak payback. For those plants Tetra Heat Pump offers a shared savings arrangement, the structure usually called an ESCO or energy service model: the supplier funds and installs the system and is paid from the savings it produces, rather than the plant raising a capital sanction of its own. Terms are settled project by project, so raise it early with the supplier rather than treating it as an off-the-shelf product, but if what blocks you is the capital approval and not the arithmetic, it changes which committee the project has to clear.

Where does the heat come from once the burner is off?

A heat pump does not create heat; it only moves heat from one place to another. The design therefore has to start from whatever the plant is already throwing away.

The candidate sources are usually already in the yard: cooling tower return water, hot effluent, compressor heat rejection, refrigeration condenser heat, and warm exhaust air. A water source is worth hunting for, because it is warmer and steadier than ambient air and the machine works less to lift it. Where no usable stream exists, an air source unit is the fallback. If the lift from source to output is too large for one stage, a cascade arrangement splits it across two.

Some plants have the source and the load at the same time and do not notice. An automotive paint shop holds its electrodeposition bath at 28 to 32°C, which is a cooling duty, while the pretreatment line next to it wants 55 to 80°C. One machine can serve both ends, and the economics of doing so are different from those of heating alone.

Tetra Heat Pump units run on refrigerants including R1234ze and R245fa, hold output to ±0.5°C, and are built in air source, water source and cascade configurations, so the source is a design decision, not a limit on who can supply you. There is more on the equipment and how it integrates and on tying it into existing plant controls.

What does the extra electrical load trigger?

This is the part of the sequence that catches people by surprise, because it rests with the DISCOM rather than with the equipment supplier, and it runs to its own timetable.

Moving a duty from fuel to electricity raises the sanctioned load. If the increase exceeds your headroom you are applying for enhancement, and in Maharashtra the published charges look like this.

Item, MSEDCL Schedule of Charges	Charge
Application and processing, HT up to 33 kV, load enhancement included in the annexure	₹2,660
Service connection, HT 11 kV up to 1,000 kVA, overhead	₹2,38,110
Metering cubicle with CT and PT, 11 kV	₹91,500

Those are the rates effective 1 April 2023, GST extra, and every state publishes its own schedule.

The larger number is not on that list. Maharashtra sets the security deposit at twice the average billing cycle and recalculates it annually, so a heat pump that raises the monthly bill pulls through a proportionate increase in deposit at the next revision. Gujarat is harsher: where additional demand is sanctioned, the deposit is computed as if the whole load were a new service, not just the increment. Neither figure appears in an equipment quotation, and both are cash.

Timing is a soft commitment, not a guarantee. The MERC Supply Code requires the licensee to endeavour to release a connection within 7 working days where no right of way is needed and 15 where it is, and the word in the regulation is endeavour. The same code requires the consumer to provide land, or a room on lease, where a distribution transformer has to sit on site, which is a site-planning consequence almost nobody anticipates at proposal stage.

One more, specific to Maharashtra. HT consumers have been billed per kVAh since 2020, a quarter of consumers above 200 kVA run power factor below 0.90 and under 0.5% actively manage it. A large compressor makes that worse, so automatic power factor correction belongs in this project and not in a later one.

What stays on the boiler?

A good deal more stays on the boiler than most vendor pages are willing to admit, and stating this plainly is the only thing that makes the rest of this page worth reading.

Saturated steam at pressure, curing ovens, drying ovens and every duty above the heat pump’s output ceiling stay on the fired system. So the realistic outcome in a gas-fired Indian plant is a partial switch: the heat pump takes the loads below 100°C, the boiler is retained for the balance and as backup through the first year, and the gas bill falls a long way short of zero.

There is a regulatory prize in that 100°C line. A hot water circuit below 100°C is not a registered boiler under the Indian Boiler Regulations, and the certified attendant on every shift and the annual inspection shutdown go with the registration. Do not read it as a blanket benefit. Above 100°C the water is at saturation pressure and the position depends on vessel design and on your state Boiler Directorate, so scope it against the duty you are actually moving and confirm it locally.

What happens to the fuel bill, and where does this argument stop working?

Against the fuels that a heat pump genuinely beats, namely PNG, LPG, furnace oil, LDO and diesel, the saving on the displaced load runs between 40 and 70%. Where a given plant lands inside that range is set by the COP it achieves, which is set by the duty.

The cleanest test is the breakeven COP: your electricity price per kWh divided by the cost of a useful kWh of heat from your current fuel. Against gas and furnace oil in India that ratio is 1.0 to 1.2, so the machine has to do very little more than work, and every point of COP above the ratio is margin, with the gas case worked through in full against a PNG boiler. Against coal it is 3.3 to 6.5.

COP itself depends on the lift, not on the output temperature alone. Tetra Heat Pump water source units reach COP 4.5 to 5.2 at 60°C output, and performance falls as output temperature rises toward the 120°C ceiling. Independently measured performance in Indian conditions is about 2.26 at 110°C output and about 2.0 at 120°C. Both ends are real, they are the same curve, and a page that quotes only one of them is not describing a machine you can plan around. This is why the answer to how much you will save is always two questions: which fuel are you displacing, and at what output temperature.

Where this stops working is solid fuel. A breakeven of 3.3 to 6.5 is out of reach for a 120°C machine on grid power, so a plant burning coal or briquette will not save money on the fuel line by switching, and any page that tells you otherwise will be caught by the first competent energy manager who reads it. Plants do still switch off solid fuel, for compliance, air quality, labour and customer audit reasons, and those are the honest grounds for the conversation.

Does production stop while you change over?

Production does not stop for the installation itself, which is carried out alongside the existing system while the boiler continues to carry the plant. The stoppage you have to plan for is the tie-in, and it belongs in an existing maintenance window rather than in a new one.

Keep the boiler live behind the heat pump through commissioning and through the first full season of ambient conditions. That is not a comment on reliability, it is how any utility change should be run: you want the fallback available while you are still learning the new system’s behaviour at your own load profile.

Controls are the part that decides whether the plant actually adopts it. Tetra Heat Pump systems integrate with BMS, SCADA and PLC networks, including Siemens and Allen-Bradley platforms over Modbus and BACnet, so the machine appears in the control room the operators already use rather than as a separate panel somebody has to remember to check. Tetra Heat Pump has more than 200 installations across India, and the published service response is 24 to 48 hours.

Working out the sequence for your plant

Begin with the load list, because nothing useful can happen until that list exists. The calculator takes your source and output temperatures, your heat demand and the fuel you burn today, and gives you a first pass at the comparison for one duty.

If that block of load looks worth moving, the next step is someone reading your metered profile, not a quotation, and you can get that started here. Background on the equipment and the company is on the industrial heat pump manufacturers page.