Note: This is not my mod. This is merely an update to 0.18, the current most recent Factorio version, as the original author has not updated it. If the mod author updates theirs and/or asks for this to be removed, it will be taken down. Posted under the same license as the original mod with respect to the author. In the update, I did have to update the pollution values to get them to work, as well as change 'emissions' to 'emissions_per_minute'. I think I got the pollution values for each item correct, but let me know if anything is inaccurate.
Original Author: https://mods.factorio.com/user/Degraine

Edit: Original mod is updated for 0.18, so please use that one instead.

Some additional means of generating steam.

Electric Boiler
Uses electricity to generate 165°C steam
Consumes up to 4.2MW of power
Electric boilers are designed to produce steam from solar power for storage or transport, or in the case of coal liquefaction, where 500°C steam would be wasted. They can produce up to 100 steam/second, enough to supply ten oil refineries processing coal. Recommended for use with Steam Cracking.

Oil-fired Boiler
Burns heavy oil, light oil, or petroleum gas to generate steam
Otherwise identical to standard boilers
Power Plant & Oil-fired Power Plant
Burns normal fuels (wood, coal, solid fuel, etc) or oil products (heavy/light oil, petroleum gas) to generate heat
Heat can be used to generate 165°C steam in low heat exchangers
Maximum temperature of both buildings is 450°C
Halved pollution output, +40% efficiency
The power plants are higher-efficiency burner power producers. They have a hefty energy investment at first, but will gradually pay off in the long run with lower total pollution and improved energy efficiency, and do not endlessly consume fuel like a nuclear reactor will. They cannot be used to generate high-temperature steam, that is reserved for the nuclear reactor.

A single power plant by itself can supply enough heat for six low temperature heat exchangers, which can supply four steam engines each, for 21.6MW of generating capacity. Low temperature heat exchangers can be connected on a nuclear-powered heat line to produce 165°C steam as well, with better efficiency than an electric boiler.