Realistically, most of the teaching jobs for foreigner are for 'oral' English only. There are very few people teaching at a high level in their own fields relative to the total number of teachers in China.

It's probably worth remembering the reason for the 'foreign expert certificate' - theoretically no foreign person can do a job if it can be given to a Chinese person. So, you'd need to be able to persuade the authorities that you have knowledge and skills that your employer cannot find among local graduates.

That doesn't mean you can't try - if I were you, I'd start by contacting universities from outside China that have programs in partnership with Chinese universities. Failing that, I'd start looking at what Nigerian companies have close business relationships with Chinese companies and try to get a foot in the door that way.

Good luck.

While what MissA said is true, there are universities around that teach Engineering in English... however, I'd bet my entire life's savings that any decent university would require you to be somewhat more than a 'graduate' engineer - ie, have a lot of experience.

Again, good luck!